thesis extension oxford

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• Graduate school
• Information and resources for supervisors

Writing up, Submission and the Viva

This section provides information about Writing up, Submission and the Viva, including links to relevant regulations and useful information and resources.

Contents of this section (please scroll down to see each):

INTRODUCTION AND KEY STAGES OF COMPLETION

KEY UNIVERSITY DOCUMENTS AND REGULATIONS

DIVISIONAL REGULATIONS, GUIDANCE AND FORMS

OTHER USEFUL RESOURCES

introduction and key stages of completion

DPhil students are usually expected to submit their thesis within three or four years (12 terms) of being admitted as Probationer Researcher Student (PRS). Part time DPhil students are usually expected to submit their thesis within eight years (24 terms).

MSc by Research (MSc(R)) students are usually expected to submit their thesis within two or three years of being admitted as Probationer Research Student (PRS), although some may complete within one year.

The expected completion date for both full time and part time students is six months after the submission date; this is to allow for the Viva examination to take place, and for the student to complete any minor corrections and re-submit the thesis. NB these extra six months should not be used to complete any research, as the maximum submission date remains the same . 

Extensions:  Should circumstances arise where your student may need to apply for an extension, you can find information on what they should do on the page on Extensions and Suspensions .

Thesis Standard:  DPhil - The standard required for success in the DPhil examination is defined as follows: that the student present a significant and substantial piece of research, of a kind which might reasonably be expected of a capable and diligent student after three or at most four years of full time study in the case of a full-time student, or eight years in the case of a part-time student.  MSc (R):  The standard required for success in the MSc (R) examination is defined as follows: that the candidate should have made a worthwhile contribution to knowledge or understanding of the relevant field of learning after a minimum of one year or two years of full-time study.

It is important to note that at Oxford the examination assessment is completely independent of the student’s supervisor. While of course the supervisor offers support and advice, the outcome will rest on the recommendations of the examiners, and final approval by the relevant board. You should familiarise yourself with Section 7 of the University’s Policy on Research Degrees , which deals with examination.

Your department’s Director of Graduate Studies (DGS) will be able to advise you on the examination process and procedures, including guidance on examination criteria. 

As supervisor you may advise the Director of Graduate Studies if there are any special factors which should be taken into account in the conduct of your student’s examination. For example, a scientific paper may have been produced by another researcher which affects the content of the thesis, but which was published too late for it to be taken into account. You should also advise the Director of Graduate Studies if the student has any special needs that might affect their performance in the oral examination, or if any part of their work must be regarded as confidential. The Director of Graduate Studies will forward, via the Graduate Office, any appropriate information that they think should be provided to the examiners. The Graduate Office will then seek approval from the Proctors Office if required.

Form GSO.20a  provides notes and guidance for the student on the whole submission process.

Download an overview of the examination process (PDF)  from the University of Oxford website.

The key stages of completion are:

Writing the Thesis

In the MPLS Division some departments permit students to submit their thesis as an integrated thesis

You / your student should also check the examination regulations for any word or page limits.

You should work with your student to create a plan for writing up, and encourage them to start writing up early so that any hold ups or unexpected events can be absorbed more easily. 

Appointment of Examiners

It is your responsibility as the supervisor to identify and propose appropriate examiners for your student. There are normally two, one internal and one external. The internal examiner is usually a senior member of Oxford University; the external examiner usually from another research organisation. Section 7 of the University’s Policy on Research Degrees provides further information on the appointment of examiners, particularly on who may act and what might be considered as a conflict of interest.

The application for the appointment of examiners should be made no earlier than the term before, and ideally no later than 4-6 weeks before the intended submission.

You should consult with your student before making final decisions about proposed examiners, and you are encouraged to contact potential examiners informally to determine whether they are willing in principle to act and, if so, whether they are able to carry out the examination within a reasonable period of time. The process is:

• Student completes their sections of the GSO.3 , Application for the Appointment of Examiners (via My student record in student self service)
• Supervisor completes their section indicating names of the proposed examiners, and they should provide alternatives in case the preferred examiners decline to act.
• Supervisor choice of examiners is approved by the Director of Graduate Studies. (The University Regulations make reference to department, faculty or divisional board as being the decision making body in relation to examiner appointments. In MPLS this authority is delegated to the Director of Graduate Studies)
• The completed GSO.3 form is processed by the MPLS Divisional Graduate Office.
• The Exam Schools issue the formal invitations to the examiners.

submitting the thesis

Students are only permitted to submit their thesis when they have successfully completed the Transfer and Confirmation of Status milestones (Confirmation of Status is only required for DPhil Students, not for M.Sc(R) students.)

The final decision on when to submit is the student’s, noting that those funded by a research council may have a specified date by which they are expected to submit. It is of course in their interest to involve the supervisor at all stages, and to make the final version of the thesis available to you for your final comments in good time before they submit.

You should encourage your student to ensure that their standard of English is sufficient for the presentation of the thesis, and to pay particular attention to the final proof–reading. Read more information about layout and presentation of the thesis . It is the student’s responsibility to ensure their thesis has been adequately proof-read before it is submitted.   As the student’s supervisor, you should tell the student if you notice that further proof-reading is required when reading a final draft.  However, it is not your responsibility to proof-read the student’s work.  Neither is proof-reading the job of the examiners: the student should not submit a thesis which requires further proof-reading, and should employ a professional proof-reader for this purpose if necessary.

Theses should be submitted via the   Research Thesis Digital Submission   (RTDS) portal. The University’s deadline for submission is no later than the last day of the vacation immediately following the term in which the students application for the appointment of examiners was made.

Copies of the thesis should NOT be given direct to the examiners as this could result in the examination being declared void and the student could be referred to the University Proctors.

It is normally expected that the Viva examination should take place within three months of thesis submission, although there are no regulations requiring it to happen within a defined period of time. The actual date of the exam will depend primarily on the availability of both examiners; it is worth noting that more time is usually needed to arrange the date during the Long Vacation. The internal examiner is responsible for arranging the date; they will contact the student once a date has been arranged.

If your student needs to have their viva sooner than three months after submitting the thesis, they may apply for an early viva when completing the application for appointment of examiners form. The examination date requested must not be earlier than one calendar month after the date on which the thesis has been received by the Research Degrees Team  or  after the date on which the examiners have formally agreed to act, whichever is the latest. The actual date of the examination will depend primarily on the availability of both examiners. In the Long Vacation, a longer time is normally required.  It is important that your student allows sufficient time for forms to be approved and examiners to be formally invited. If sufficient time has not be given this could impact on the early examination request.

If, for any reason, examiners wish to hold a viva within four weeks of receiving their copy of the thesis, permission must be sought from the Director of Graduate Studies. The internal examiner will need to give details of the proposed arrangement and the reasons for the request. Under no circumstances will a viva normally be permitted to take place within 14 days of receipt of the thesis by the examiners.

Students and supervisors should not contact examiners themselves except to agree the date for the viva; if examiners have not been in touch within a month of receiving the thesis, the Research Degrees team  will contact them.

Your student should wear appropriate academic dress and take a copy of their thesis to the viva.

Examiners will be provided with the Memorandum for Examiners for the Degree of Doctor of Philosophy ( GS0.5 ), or Memorandum of Guidance for M.Sc Examiners ( GSO.7a ), which give information about the purpose and formal requirements of the viva, the practical arrangements, the conduct of the exam and the requirements of the examiners’ report.  They will also be sent a copy of the MPLS Division's additional notes of guidance for examiners .

For more information about regulations and the purpose of the viva,  see section 7, about examination, of the University’s Policy on Research Degrees about the viva.

DPhil (first) Examination:  Examiners must choose one of the following outcomes: 

1. Award of the DPhil (possibly with minor corrections)

2. Major corrections to the thesis

3. Reference back (for revision) for DPhil or award of the M.Sc (as the thesis stands or subject to minor corrections) as the student may choose

 4. Reference back (for revision) for the DPhil or (for revision) for the M.Sc as the student may choose

 If the student chooses to revise and resubmit for the DPhil the following options will also be available to the examiners on the next examination: 

5. Reference back (for revision) for the M.Sc only

6. Award of the M.Sc

7. Outright failure

M.Sc (R) (first) Examination : examiners must choose one of the following outcomes: 

1. Award of the M.Sc (possibly with minor corrections)

2. Reference back (for revision) for the M.Sc

If the student chooses to revise and resubmit for the M.Sc the following option will also be available to the examiners on the next examination:

3. Outright failure

Full guidance on these is set out in the University's Memorandum of Guidance for DPhil Examiners ( GS0.5 ) and Memorandum of Guidance for M.Sc Examiners ( GSO.7a ).

Deposit of hard copy thesis to the bodleian and e-theses to ora

If your student is granted leave to supplicate they are no longer required to submit a hard-bound copy of their thesis to the Examination Schools in order to graduate. This includes any students who were unable to submit a hardbound copy due to COVID-19 social distancing measures in the 2019/20 & 2020/21 academic year.

However, all candidates do need to submit an electronic copy (incorporating any amendments required by the examiners) to the Oxford University Research Archive (ORA) a minimum of five working days prior to their graduation date. Students will not be able to attend a degree ceremony (even in absentia) without doing so.

key university documents and regulations

The University’s Policy on Research Degrees

Section 7 of the University’s Policy on Research Degrees, which covers examination : 

Examination Regulations – General Regulations Governing Research Degrees

Examinations Regulations – General Regulations for the Degree of Doctor of Philosophy

Examinations Regulations – General Regulations for the Degree of Master of Science by Research

divisional regulations, guidance and forms

Examination regulations for Research Degrees in the MPLS Division

Subject Specific Examination Regulations:

• Biological Sciences (Biology)
• Mathematical Sciences (Computer Science, Mathematics & Statistics)
• Physical Sciences (Chemistry, Earth Sciences, Engineering Science, Materials & Physics)

MPLS Additional Notes of Guidance for Examiners  

MPLS student webpages on submitting your thesis and examination .

other useful resources

Some departments organise briefing and discussion sessions for their supervisors, which are useful opportunities to update yourself on regulations and processes, and to share practice and discuss experiences. Please contact your Director of Graduate Studies to find out if your department is planning such a session. 

MPLS Divisional training courses for DPhil students

Theses and dissertations

Read our guidance for finding and accessing theses and dissertations held by the Bodleian Libraries and other institutions.

Students may become aware before a deadline that they will need to submit their work late, because of illness or other urgent cause

If they do, students should ask their college (or, if a non-matriculated student, their department) to apply to the Proctors for the late submission using the Extension Form  to be excused in advance. Students will need to provide evidence, such as a letter from their doctor, and an extended deadline will be set if their application is granted. Extension requests should be for relatively short periods of time. If a student thinks they will be unable to work for a very long time, they should speak to their college about making other arrangements to delay their studies.

Proctors' Office University Offices Wellington Square Oxford OX1 2JD Email:  [email protected]

Related links

• Proctors' website
• On-course information
• Governance and policy

Submitting your thesis to ORA: Requirements

• Eligible degrees
• Requirements
• What to deposit
• Pre-deposit checklist
• Hardcopy thesis submission
• How to deposit
• Open Access
• Pre-publication concerns
• Restricted access to your thesis
• Edited/dissemination copy of your thesis
• Oxford Research Theses and predatory publishers
• Funder/sponsor requirements
• Third party copyright
• Fair dealing
• RightsLink®
• Google Maps/Permissions
• Creative Commons
• Unable to get copyright permissions
• Separate appendix
• Plagiarism concerns
• Information for Supervisors
• Digital preservation
• Visibility of your thesis
• Persistent URLS

This page outlines when a thesis can be deposited to ORA, and the requirements which must be met in order for the deposit to be eligible.

When to deposit

Current students must have been granted  leave to supplicate  following examination of their thesis to be eligible for deposit.

Theses should be deposited in good time (a minimum of five working days) in advance of graduation so that they can be processed by the ORA team.

Alumni and Oxford staff/researchers can deposit their thesis to ORA at any time.

Conditions of deposit

The following conditions must be met in order to deposit your thesis:

• The degree for which your thesis was written is eligible for deposit (see:  eligible degrees )
• The deposited file should be the final examined version as it was passed by the examiners with all corrections included (see: what to deposit)
• Inclusion of the thesis in ORA must not infringe copyright or any other rights including those rights of material included in the thesis where copyright is held by a third party. This is the responsibility of the depositor to check (see:  copyright )
• The author must agree to the ORA deposit statement for theses
• A digital version of the thesis must be submitted by the depositor (ORA cannot offer a digitisation service at the present time)
• A thesis record, including the thesis abstract, will be created for your theses and made publicly available via ORA, unless specific dispensation has been granted (see: dispensation ) 

Additionally, for current students:

• Any embargoes on access beyond 3 years must be approved by the supervisor or another appropriate person in the department which granted leave to supplicate.

For alumni and Oxford researchers/staff who graduated before the COVID-19 pandemic:

• A print copy of the thesis must have been deposited in the Bodleian Library

ORA reserves the right to refuse any item if any of these conditions are not met, or in any other exceptional circumstances.

Hardcopy Thesis Submission

Conditions regarding the deposit of physical theses to the Bodleian Libraries as detailed within the requirements surrounding a degree at Oxford have been changing. For information on physical theses deposit please see the section ' hard copy theses ' and refer to the requirements of your degree.

Oxford Glossary

Supplicate : Ask for a degree to be conferred at a degree ceremony.  E.g. candidates who satisfactorily complete a DPhil are granted ‘Leave to supplicate’, meaning they have passed.

• Oxford Glossary of terms Weblink to Oxford Glossary
• University of Oxford glossaries PDF containing a glossary of Oxford terms, acronyms and obsolete Oxford usages.
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• Last Updated: Apr 10, 2024 5:00 PM
• URL: https://libguides.bodleian.ox.ac.uk/digitaltheses

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DPhil and postgraduate open access portal

Welcome to the open access portal page for DPhils at Oxford, where we have compiled links and information specific to your work.

On this page

What applies to you, responsibilities and options, training for dphils, how to make your research open, tools and resources to help, oxford university open access publications policy.

The University’s 2018 Open Access policy applies to research students and asks them to deposit journal articles and other research outputs, including research data, into ORA.

Depositing your thesis

DPhils at Oxford will need to deposit their thesis into the Oxford University Research Archive. Learn more on the Bodleian Libraries guide to ORA.

Funded DPhil?

If your DPhil is funded your outputs (including your thesis) may be subject to your funder's open access requirements.

Back to top

UKRI-funded DPhils at Oxford

What is covered.

If you are a DPhil student who is funded by UKRI for the entirety of your DPhil, then the UKRI open access policy applies to:

• your thesis 
• publications based on your DPhil funded research during your DPhil
• publications based on your DPhil funded research after you have finished your DPhil (see below on re-use of data).

Note: After 1st January 2024, this will include monographs and book chapters.

If you are funded for a specific piece of work during your DPhil, then the UKRI open access policy applies to that specific piece of work.

Learn about UKRI’s open access policy

Official wording

The  UKRI Terms and conditions for training funding  state in section 11 Exploitation and Impact that:

11.4 Students supported by the Training Grant shall, subject to the procedures laid down by the Research Organisation, publish the results of their research, excluding theses (see TGC 11.5), funded by the Training Grant, in accordance with normal academic practice and  Our policy on open access . Publications and other forms of media communication, including media appearances, press releases and conferences,  must acknowledge the support received  from Us, quoting the Training Grant reference number if appropriate.  Please see details on how to acknowledge funding from UKRI.

Go to our templates page to find official acknowledgement wording

Grants awarded before the policy start date, and closed grants

The policy applies to a publication arising from pre-existing and closed awards if it is an in-scope research article submitted for publication on or after 1 April 2022, or an in-scope monograph, book chapter or edited collection published on or after 1 January 2024.

Thesis deposit and embargoes

You will need to deposit a copy of your thesis into the Oxford University Research Archive.

UKRI have several requirements for this that are outlined on the thesis LibGuide. 

Go to the University of Oxford thesis LibGuide

Training for Oxford DPhils depositing their thesis

Journal articles and conference papers

• have published a journal article or conference paper
• and this is during your DPhil (or after – see below about the re-use of data)
• and it acknowledges the funding from your DPhil

then the UKRI open access policy applies to this work and you may apply for funds from our Oxford-held block grant to assist with compliance. (Please note the criteria for payment and funder requirements.)

Apply to the Oxford University UKRI APC block grant

Book chapters

• have published a book chapter
• and publication is after 1st January 2024

then the post-1st January 2024 policy on book chapters will apply.

Monographs based on your thesis

There are special exemptions to the 1st January 2024 open access monograph policy for "UKRI issued training grant" students who are publishing a monograph based on their thesis.

You do not need to follow the open access monograph section of the policy . However, you are allowed to apply for open access funding from the monograph fund hosted by UKRI either through your new institution or as a solo researcher. This would allow you to benefit from an open access monograph.

Publishing works unrelated to your UKRI DPhil funding

If, for example, you publish an article that is a re-written version of your masters dissertation and UKRI did not fund this masters, then UKRI will not be acknowledged on that paper and therefore you do not need to follow the policy.

You can, of course deposit the article into ORA for ‘green’ open access or make use of publisher deals to publish ‘gold’ open access if you wish.

If you feel you need to acknowledge your research funding, then the policy will need to be followed for applicable outputs.

Publishing outputs based on UKRI-funded DPhil data

If an output is a result or adaptation of research that you undertook while having UKRI funding, then that output needs to comply with UKRI open access policy.

Any subsequent work created by building on data collected during a DPhil is considered a secondary project and would not need to comply.

For example, if a UKRI-funded DPhil

• writes a thesis based on research they carried out while they were UKRI funded
• makes their thesis open access in accordance with the rules of their training grant
• goes on to do additional post-doc research funded from another source, though building on the data collected during their DPhil

then they wouldn’t be subject to the UKRI policy, because the second research project, even though it draws on existing data, is a separate exercise.

However, if they

• adapt the thesis into a journal article using content which is broadly the same as the thesis
• acknowledge funding received during their doctorate
• are using data collected during the DPhil which has not yet been used for their thesis or any published work

then they ought to comply and acknowledge UKRI.

Funding for publication

If you are publishing articles and conference papers that are in scope of the UKRI open access policy (see above) you may apply for funds from the block grant.

Note payment exemptions and fund status.

If you are publishing in a journal covered by an Oxford-signed publisher deal during the duration of your DPhil, you should submit using your @ox.ac.uk email address and make use of the deal.

Note: many deals will not be available to you after you have left the University.

If you are publishing a monograph based on your thesis you may apply for open access publication funding from the UKRI managed monograph fund.

Note: there is no guarantee of funding as this output is ‘out of scope’ for the policy.

The REF and DPhils

DPhil students may publish outputs that are later submitted to the REF, but those produced while they were a student are exempt because they were not employed by a UK higher education institution at the time of submission for publication.

Unfunded Dphils

DPhils who are not in receipt of funds for open access payments can achieve open access through other routes.

Learn more about unfunded routes to open access

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Definition of extension noun from the Oxford Advanced Learner's Dictionary

increasing influence

• the extension of new technology into developing countries
• a gradual extension of the powers of central government
• The bank plans various extensions to its credit facilities.
• My home life was becoming no more than an extension of my job.
• The company sees brand extensions as a means of tempting back customers.
• The team appraisal is a logical extension of the individual appraisal interview.
• This new job is a further extension of his role as a manager.
• considerable

Questions about grammar and vocabulary?

Find the answers with Practical English Usage online, your indispensable guide to problems in English.

of building

• They're building an extension to their house.
• refurbish/​renovate/ (British English) do up a building/​a house
• convert a building/​house/​room into homes/​offices/ (especially North American English) apartments/ (British English) flats
• extend/​enlarge a house/​building/​room/​kitchen
• build (British English) an extension (to the back/​rear of a house)/ (North American English) an addition (on/​to something)/ (British English) a conservatory
• knock down/​demolish a house/​home/​building/​wall
• knock out/​through the wall separating two rooms
• furnish/​paint/ (especially British English) decorate a home/​a house/​an apartment/​a flat/​a room
• be decorated in bright colours/​in a traditional style/​with flowers/​with paintings
• paint/​plaster the walls/​ceiling
• hang/​put up/​strip off/​remove the wallpaper
• install/​replace/​remove the bathroom fixtures/ (British English) fittings
• build/​put up shelves
• lay wooden flooring/​timber decking/​floor tiles/​a carpet/​a patio
• put up/​hang/​take down a picture/​painting/​poster/​curtain
• do (British English) DIY/​carpentry/​the plumbing/​the wiring
• make home improvements
• add/​install central heating/​underfloor heating/​insulation
• fit/​install double-glazing/​a smoke alarm
• insulate your house/​your home/​the walls/​the pipes/​the tanks/ (especially British English) the loft
• fix/​repair a roof/​a leak/​a pipe/​the plumbing/​a leaking (especially British English) tap/ (North American English usually) faucet
• block/​clog (up)/unblock/​unclog a pipe/​sink
• make/​drill/​fill a hole
• hammer (in)/pull out/​remove a nail
• tighten/​untighten/​loosen/​remove a screw
• saw/​cut/​treat/​stain/​varnish/​paint wood
• extension to
• a planned two-storey extension to the hospital
• He's been granted an extension of the contract for another year.
• a visa extension
• She was given an extension to finish writing her thesis.
• (British English) The pub had an extension (= was allowed to stay open longer) on Christmas Eve.
• He's applied for an extension of his visa.
• The player has signed a five-year contract extension.
• We have an extension in the bedroom.
• What's your extension number?
• Can I have extension 4332 please?
• I'll give you my extension number, so you can phone me directly.

making something longer/larger

• The extension of the subway will take several months.
• extensions to the original railway track
• These extensions are very easy to use and won't damage your own hair.

college/university

• La Salle Extension University
• extension courses
• The extension .doc indicates a word-processing file.
• [countable] (also extension lead (both British English) , North American English extension cord ) an extra length of electric wire, used when the wire on an electrical device is not long enough
• The blame lies with the teachers and, by extension, with the Education Service.

Other results

• extension leads

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Article Contents

Introduction, materials and methods, supplementary material, acknowledgments.

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Extension of the geographical range of the primary burrowing crayfish Cambarus strigosus Hobbs, 1981 (Decapoda: Astacidea: Cambaridae) in South Carolina

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Zanethia C Barnett, Mickey R Bland, Gregory Myers, Zachary J Loughman, Extension of the geographical range of the primary burrowing crayfish Cambarus strigosus Hobbs, 1981 (Decapoda: Astacidea: Cambaridae) in South Carolina, Journal of Crustacean Biology , Volume 44, Issue 2, June 2024, ruae021, https://doi.org/10.1093/jcbiol/ruae021

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Knowledge of the geographical distribution for many primary burrowing crayfishes is often limited to information presented in species descriptions or field notes associated with epigean crayfish surveys. Cambarus strigosus Hobbs, 1981 , a rare primary burrowing crayfish, was collected as part of a survey of the Sumter National Forest, South Carolina (SC), USA. Prior to this discovery, C. strigosus appeared to be endemic to mid-reaches of the Broad River Drainage in Georgia (GA). We conducted additional field sampling in SC and GA and used mitochondrial DNA (mtDNA) to compare the relative genetic distance between individuals across all populations in an effort to determine the identity of the specimens collected. Genetic data indicated that the crayfish collected in SC was C. strigosus, with one shared haplotype between SC and GA populations. Our genetic results exhibited geographic structuring and indicated that SC populations have a specific haplotype unique to them, providing strong evidence that SC populations are not introduced. Two additional SC records of C. strigosus from 1983 housed in the US National Museum were examined and determined to be C. strigosus . With these records, we hypothesized that like in GA, the distribution of C. strigosus in SC is limited to riparian habitats associated with the Savannah River Drainage. While the range of this species has been extended, it is still limited to small portions of this drainage. Thus, further sampling to determine the true extent of C. strigosus distribution within SC along with conservation efforts are needed to protect this globally rare species.

Crayfishes have received concerted survey efforts across eastern and central North America over the past two decades ( Taylor et al., 2019 ). Several species, most of which are epigean species that live in perennial waterways, have had significant range extensions as a result of these efforts ( Loughman et al., 2018 ; Glon et al., 2018 , 2022 ),. Nonetheless, crayfishes occur in numerous habitat types (e.g., riparian zones, wetlands, caves; Hobbs, 1981 ), where it is often difficult to collect and document crayfishes ( Loughman et al., 2018 ). Species inhabiting riparian zones and wetland environments with active hydroperiods have evolved mechanisms to follow groundwater levels as they retreat underground during dry seasons. These species are referred to as secondary or primary burrowers (hereafter referred to as burrowing crayfishes; Hobbs, 1981 ). Collecting burrowing crayfishes can be difficult, time intensive, are often limited due to time and funding, and requires investigators to learn the intricacies of burrow excavation. These difficulties have resulted in large knowledge gaps for many burrowing crayfishes.

The extent of our knowledge for many burrowing species is limited to natural history notes included in species descriptions. Another problem is that investigators often spend considerable time identifying the species in question. Recent genetic work indicates that cambarid crayfishes likely exhibit cryptic diversity that can only be captured through genetic techniques ( Hurt et al., 2019 ; Glon et al., 2022 ; Thoma et al., 2023 ) that warrants the use of these methods to confirm identification.

Documentation of new populations of burrowing crayfishes is still occurring, with discoveries made yearly. This increased effort has resulted in the description of several undescribed species ( Schuster et al., 2015 ; Glon et al., 2019 , 2020a ; Loughman et al., 2019 ). In addition to the description of new taxa, burrowing crayfishes have had significant range extensions noted over the past decade. Loughman et al. (2018) noted Creaserinus fodiens ( Cottle, 1863 ) in northwestern Pennsylvania for the first time in 2016, while Glon et al. (2022) confirmed that Lacunicambarus nebrascensis ( Girard, 1852 ) (formerly Cambarus diogenes ) still occurred in the Rocky Mountain foothills of Wyoming, where it was thought to be extirpated. Cambarus monongalensis Ortmann, 1905 , an iconic species due to its blue coloration, was first documented in Ohio in 2020 ( Glon et al., 2020b ). Another example of the discovery of a new population occurred in the Long Cane Ranger District, Sumter National Forest (SNF), South Carolina (SC) in 2020. During an intensive survey to determine the presence of Distocambarus Hobbs, 1981 in, a burrowing Cambarus species was encountered in a lowland field managed for wildlife. This crayfish was identified as Cambarus strigosus Hobbs, 1981 , the lean crayfish, following Hobbs (1981) . According to state and federal records and reports, as well as peer-reviewed literature, C. strigosus appeared to be endemic to the mid-reaches of the Broad River Drainage in Georgia (GA). Collection of C. strigosus in SNF they represented a significant range extension for this poorly known species. Subsequent surveys of SNF bottomland habitats along the Savannah River confirmed additional C. strigosus colonies, which warranted an effort to determine 1) if the specimens belonged to C. strigosus or to an undescribed species, and 2) if C. strigosus had been collected before our efforts and documented in SC.

Field collections

Collections associated with the discovery of C. strigosus in SC occurred February 29, 2020, in the Long Cane Ranger District of SNF, McCormick County, SC ( Table 1 ; Fig. 1B ). Crayfish were collected by excavating burrows by hand. Burrows were excavated until burrow chambers or water was reached. If water was reached before reaching the chamber, burrows were plunged vigorously, and time was afforded to allow crayfish to respond. Any crayfish present would normally rise to the surface within 1–5 min following plunging, at which point it was captured.

Locations, habitat, elevation, and number of individuals of Cambarus strigosus collected during 2020 (*) and 2022 in South Carolina and Georgia, USA.

Study area with sampling locations and historic sites represented by dots, and known range of Cambarus strigosus represented by a gray polygon. Georgia sites ( A ), all sites sampled on the Sumter National Forest ( B ), and historic SC samples ( C , D ).

Because there was only one C. strigosus mitochondrial COI sequence publicly available in the National Center of Biotechnology Information (NCBI) GenBank database, additional field collections were made in spring of 2022 from C. strigosus current range in GA and the Long Cane Ranger District in SNF, SC ( Fig. 1A , B ) to confirm that collected SC specimens belong to this species. Individuals of C. strigosus were collected between February and April 2022 via hand excavations from one site in GA and six sites in SC ( Table 1 ). The GA site, six miles from the type locality of the species, was a field along a tributary to the Broad River ( Hobbs, 1981 ). The type locality was sampled, but no C. strigosus were collected. Sites in SC were all within the SNF and included three field and three forest sites. We recorded crayfish identification, sex, reproductive form, and total carapace length (TCL) immediately after sampling. We preserved legs in 95% ethanol for genomic analyses. We also preserved voucher specimens in 70% ethanol for future morphometric analyses and deposited the specimens in the North Carolina Museum of Natural Sciences, Raleigh, NC.

Collection of genetic data

We extracted genomic DNA from crayfish-leg tissue using a DNeasy Blood and Tissue Kit (Qiagen, Germantown, MD, USA), following the manufacturer’s recommendations. We amplified a portion of the mitochondrial cytochrome oxidase subunit I (COI) gene via polymerase chain reaction, using primers LCO1490 and HCO2198 ( Folmer et al., 1994 ).

Amplifications of polymerase chain reactions were performed in a final volume of 15 μl containing 1.5 μl genomic DNA, 3.0 μl 5× buffer (Promega, Madison, WI, USA), 1.2 μl MgCl2 (25 mM, Promega), 2.5 μl deoxynucleotides (1.25 μM, Promega), 0.75 μl bovine serum albumin (10 mg μl –1 ; New England Biolabs, Ipswich, MA, USA), 4.4 μl dH2O, 0.15 μl Go-Taq DNA polymerase (5U μl –1 , Promega), and 0.75 μl of each primer (10 μM). Thermocycling conditions were 95 °C for 2 min (1 cycle), 95 °C (denaturing) for 30 s, 50 °C (annealing) for 30 s, 72 °C for 1 min (35 cycles), and a final extension at 72 °C for 2 min (1 cycle). To assess the quality and estimate the size (in base pairs (bp)) of amplified products, we used agarose gel electrophoresis and compared amplified products to a 100-bp ladder. Amplified products were purified using ExoSAP-IT® (Affymetrix, Santa Clara, CA, USA) and sequenced on an Applied Biosystems 3730xl DNA Analyzer at Azenta Life Sciences (Burlington, MA, USA). Sequence chromatograms were manually edited, aligned, and assessed for quality by translating DNA to amino acids to confirm the absence of premature stop codons, using MEGA v.11 ( Tamura et al., 2021 ). All sequences generated in this study are available from NCBI GenBank under accession numbers PP555610–PP555634 ( Supplementary material Table S1 ). We also used publicly available mitochondrial COI sequence data from the NCBI GenBank database.

Sequence analyses

We compared the relative genetic distance between C. strigosus collected in GA and SC using two approaches to verify the identity of the collected material. We used Mega v.11 to assess pairwise nucleotide differences between each specimen using the maximum likelihood method at uniform rates, with gaps and missing data treated as pairwise deletions ( Beerli & Felsenstein, 2001 ; Tamura et al., 2021 ). Additionally, we assessed pairwise nucleotide differences between SC and GA specimens by using the same methods stated above. We then estimated phylogenetic relationships among haplotypes using statistical parsimony networks ( Clement et al., 2000 ) calculated using PopART v.1.7 ( Leigh & Bryant, 2015 ). Haplotype networks can better illustrate genetic divergence within species than do bifurcating phylogenetic trees, especially when multiple haplotypes are derived from a single ancestral sequence ( Templeton et al., 1992 ).

Additional specimen determination

We examined of museum collections and digital records to further verify the identity of the specimens collected: digital databases for the North Carolina Museum of Natural Sciences, United States National Museum, Eastern Kentucky University crayfish collection, Illinois Natural History Survey crustacean collection, South Carolina Heritage Program Database, West Liberty University astacology collection, as well as the Illinois Natural History Surveys American Crayfish Atlas website ( https://americancrayfishatlas.web.illinois.edu/ ).

$We collected one female and two juveniles of C. strigosus in 2020 from SC ( Fig 2 ),and 92 (7 reproductive (form I) males, 20 nonreproductive (form II) males, 41 adult females, 24 juveniles) also from SC and 15 (1 form I male, 5 form II males, 9 females) from GA. We used the species description by Hobbs (1981) for identification. Diagnostic characters included the noticeable slender appearance of C. strigosus as compared to congeners C. within the coastal plain region, a single pair of fixed spines on the uropod and coloration ( Fig. 3 ).

Cambarus strigosus showing the species unique, diagnostic color pattern. Photograph by Z. Graham, West Liberty University.

Morphological characters used to identify Cambarus strigosus specimens in South Carolina; all characters from Hobbs (1981) . Slender chelae ( A ) and narrow carapace ( B ) and abdomen ( C ) as compared to sympatric species; scabrous telson with single pair of fixed spines ( D ). Photograph by G. Schuster, Eastern Kentucky University.

We obtained mitochondrial COI sequences from 26 individuals of C. strigosus , 16 from SC and 10 from GA (1 sequence from NCBI, GenBank accession number JX514445.1; Brienholt et al., 2012 ), with a final alignment of 481 bp. The alignment contained 33 polymorphic sites and 12 haplotypes. Haplotype diversity (Hd) was 0.86 and nucleotide diversity ( π ) 0.023. Pairwise nucleotide distance ranged 0.000–0.094 (median 0.02). The mean pairwise nucleotide distance between groups was 0.047, within groups 0.013 and 0.028 for SC and GA, respectively. The haplotype network for C. strigosus displayed strong geographic structure indicating limited dispersal and gene flow ( Fig. 4 ). Five haplotypes were unique to SC, six to GA. Nonetheless, one SC haplotype showed only a three-mutation difference from the most common GA haplotype. Additionally, there was one shared haplotype between C. strigosus individuals from GA ( N = 1) and SC ( N = 8), indicating that gene flow occurred between SC and GA C. strigosus populations.

Cambarus strigosus ( N = 26) haplotype network based on 481-bp mitochondrial COI sequence alignments. Each circle represents a unique haplotype. Lines connecting haplotypes indicate a single mutational difference between haplotypes, with dashes along lines representing the number of mutational differences, each dash corresponding to one mutation. The size of each circle is proportional to the frequency with which that haplotype was sampled. SC, South Carolina samples; GA, Georgia samples.

Additional C. strigosus records

Two SC records for C. strigosus were documented in 1983. Both records were retrieved through use of the INHS Crayfish Atlas tool housed in the United States National Museum, but we were unable to retrieve either record. USNM 206336 specimen was collected in a seepage area in Abbeville County, SC ( Fig 1C ) and USNM 206261 from a bottomland swamp in Aiken County, SC ( Fig. 1D ). Both records were collected by P.H. Carlson and identified as C. strigosus in 1983 by H. Hobbs Jr. We studied the USNM specimens and determined to be C. strigosus based on the diagnostic features provided by Hobbs (1981) . These records proved to be the first published for C. strigosus from SC.

Crayfishes have been recognized since the mid-1990s as one of the most imperiled taxa on our planet ( Taylor et al., 1996 ). Since then, additional global ( Richman et al. , 2015 ), national ( Taylor et al., 2007 , 2019 ), and regional (southeastern USA; Loughman & Fetzner, 2015 ; Elkins et al., 2019 ) reviews have supported such assumption. A major driver of imperilment for cambarid crayfishes is their high level of endemism ( Taylor et al., 2007 , Loughman & Fetzner, 2015 , Richman et al., 2015 , Taylor et al., 2019 ). Endemics have long been identified by conservation biologists to suffer higher levels of imperilment than wide-ranging species ( Caldecott et al. , 1996 ). Determining if endemic taxa are as narrowly distributed as they appear justifies survey efforts not only for crayfishes, but for other understudied taxa as well.

Given their limited dispersal abilities, many burrowing crayfishes are classic examples of narrow endemic taxa. It is important to determine if their perceived endemism is real and not an artifact of under-sampling or lack of reporting. Cambarus strigosus was described by Hobbs (1981) from GA in the early 1980s from specimens collected from five sites in Elbert, Oglethorpe, and Wilkes counties. Skelton (2016) increased the number of sites to 16in the same counties. Based on these results, C. strigosus appeared to be endemic to GA. Unfortunately, C. strigosus collections in SC from the 1980s were not reported to state or federal agencies, or published in a report or journal, and hence these records were overlooked. Our search of historical records, along with our collections and subsequent genetics results, show that C. strigosus is not limited to three GA counties, and has a potentially wider range in SC than it does in GA.

One explanation for C. strigosus presence in SC is anthropogenic introduction. Burrowing crayfishes have been translocated by humans and established extralimital populations in the mid-Atlantic US ( Foltz et al., 2018 , Allison et al., 2021 ). Our genetic results showed geographic structuring and indicated that SC populations have specific haplotypes unique to them. These results suggest that the SC population is not undergoing founder effects or bottleneck, which is common in introduced populations where a new colony is started from a few members of the original population leading to low genetic diversity ( Wilson et al., 1999 ; Astanei et al., 2005 ; Herborg et al., 2007 ). Additionally, mtDNA markers are substantially more sensitive to founder effects and bottlenecks because of a fourfold lower effective population size compared with nuclear DNA markers ( Birky et al . 1983 ). Thus, the haplotype structure of the SC C. strigosus population provides strong evidence that these populations SC are native and not introduced. We suggest that, like in GA, the SC distribution of C. strigosus is limited to riparian habitats associated with the Savannah River. Bottomland swamps are notoriously difficult to sample for crayfishes and often are under-sampled when compared to stream crossings, roadside wetlands, and roadside ditches. All current SC records of C. strigosus are from open fields and bottomland habitats. Sampling extensive tracts of bottomland habitat often requires permission from landowners and the US Forest Service which complicates field investigations. We are currently unsure if C. strigosus occurs in roadside ditch habitats, but no specimens have so far been collected from these environments.

Roadside ditches are easier to sample, and therefore much more accessible to biologists once collection permits are obtained. Field sampling throughout the region by ZCB and ZJL for species of Distocambarus , which prefer open habitats as well as anthropogenic habitats like roadside ditches. These crews sampled roadside ditches within 100 m of the Abbeville County record of C. strigosus , but individuals were missed perhaps because of the preference of bottomland hardwoods habitats by the species.

Understanding the geographical range of species is particularly important for the conservation and protection of imperiled taxa. State record publications serve as documents that can be used by both state and federal-level biologists to justify immediate conservation attention. While publications of this nature do not normally carry high impact factors, and often do not help to increase the h-index scores of authors, their utility in conservation can be immense.

An example of conservation efforts due to a particular published report of the range extension of a crayfish species is the short communication of Loughman et al. (2018) documenting the burrowing crayfish C. fodiens in Pennsylvania. This report showed that C. fodiens was one of the rarest crayfishes in Pennsylvania, which resulted in making funds available for additional distributional studies ( Allison et al., 2022 ) that ultimately led biologists to list the species as a state-endangered species ( Lieb, 2022 ). As a result, it

Our study will hopefully lead attention for conservation efforts for C. strigosus in SC. The species has been identified by SNF biologists at the federal level as a species worthy of tracking (K. Whalen (USFS), personal communications). Dedicated surveys should occur outside of Forest Service lands to determine the actual distribution of C. strigosus in SC. At least some C. strigosus populations will need to be considered for protection and studied given the presence of the species in SNF.

Supplementary material is available at Journal of Crustacean Biology online.

S1 Table. GenBank database accession numbers for each sequence and state where collected.

We thank the following individuals for assistance with field collections K. Whalen (USFS), E. Choice (volunteer), and M. Stubbs, H. Wells, J. Krochmal, A. Shannor, A. Oppedisano, and J. Hartley (West Liberty University), and C. Smith (USFS) for editing the DNA sequences and creating maps for publication. We also thank the USDA Forest Service for funding. We also acknowledge the two anonymous reviewers for their insightful comments and suggestions.

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