Turtles: The gender issue.

 Have you ever wondered what it would be like if the entire population was one sex? Well, turtles might soon find out.

Endangered Loggerhead Turtle Caretta caretta (Anonymous 2013)

Turtles have been around for over 100 million years and have survived various climates, ice ages and even temperatures 4 degrees warmer than today (Hirayma et al 1994), (NOAA 2008) and (Spotila et al 2000). Despite this, marine turtle populations have declined to the point where six of the 7 species of marine turtle have become threatened or endangered (Department of the Environment 2015).

So how is climate change threatening the future of marine turtles?

Critically endangered Hawksbill turtle Eretmochelys imbricata (Freund 2015)

 The gender issue

The vulnerable green sea turtle Chelonia mydas, (Harasti 2015)

There are three ways gender is determined in turtles: genetic sex determination (GSD) and temperature dependant determination (TSD) and thermo-sensitive genetic sex determination (Valenzuela et al 2014). Like most reptiles, the majority of turtles have temperature dependent sex selection (TSD). This means that temperature during egg development determines gender. For most TSD species, an increase in temperature increases the proportion of female hatchlings. 

Vulnerable Flatback turtle Natator depressus (Reinhold 2013)

For most marine turtles, a global increase of less than 3 degrees could cause populations to become 100% female (Hawkes et al 2007). With global temperature expected to rise anywhere between 2-7 degrees in the next 100 years, turtles could become extinct within the next 20-50 years (Tapilatu et al 2013) and (Fuentes et al 2010). Luckily there are some ways turtles have adapted to this. 

Behavioral adaptations to climate change.

Critically endangered baby leather back turtle Dermochelys coriacea (Leonard 2012)

For species such as the green turtle Chelonia mydas which is currently 95% female, breeding behaviour has masked the effects of TSD. Astudy by Wright et al (2012) found that male turtles visit breeding grounds more often than females meaning that on average there was 1.4 males to every fecund female. Increased temperature has also caused a delay in nesting by ten days (Weishampel et al 2008).

Genetic adaptations to climate change. 

Genetic gender selection Black marsh turtle Seibenrokiella crassicollis (Hakim 2011)

Some turtle species have evolved GSD whereby turtle gender is determined by chromosomes instead of temperature (Carr and Bickham 1981) and (Valenzuela 2008). This has allowed these species to completely avoid the gender issue. However, there are variations where even GSD can be affected by temperature change (Valenzuela et al 2014). There are also variations in TSD where temperature change either above or below the optimum can cause gender bias. This allows turtles to maintain a balance through natural climate fluctuations (Ewert et al 2005).

Endangered Olive Ridley turtle Lepidochelys olivacea (Nature 2007)

Want to read more about TSD in turtles? Check out these sites: 

http://onlinelibrary.wiley.com/doi/10.1002/jez.1402700103/abstract

http://www.ncbi.nlm.nih.gov/pubmed/15066448

http://onlinelibrary.wiley.com/doi/10.1002/jez.1402600117/abstract

Thankyou for reading.  :)

Check back next week for more information on how climate change is affecting marine life. 

References

Carr J, Bickham J 1981, ‘Sex chromosomes of the Asian black pond turtle, Seibenrokiella crassicollis (testudines Emydidae)’,  Cytogenetics and cell genetics, vol.31, no. 3, pp. 178-83, viewed 29/3/15 url<http://www.ncbi.nlm.nih.gov/pubmed/7326996>

Department of the environment, year unknown, Australian government, viewed 2/4/15 <http://www.environment.gov.au/marine/marine-species/marine-turtles>

Ewert M A, Jackson D R, Nelson C R 2005, ‘patterns of temperature-dependant sex determination in turtles’, Journal of experimental zoology, vol.270, no. 1, pp.3-15, doi: 10.1002/jez.1402700103

Fuentes M M P B, Limpus C J Hamann M 2010,”vulnerability of sea turtle nesting grounds to climate change”, Global change biology, vol. 17, no.1, pp.140-153, doi: 10.1111/j.1365-2486.2010.02192.x

Hawkes L A, Broderick A C, Godfrey M H, Godley B J 2007,' Investigating the potential impacts of climate change on a marine turtle population', Global Change Biology, vol.13, pp.923-932 Doi: 10.1111/j.1365-2486.2007.01320.x

Hirayma R 1994, “Phylogenetic systematics of Chelenoid sea turtles”, The Island Arc, vol.3, pp.270-284 viewed 2/4/15, http://scholar.google.com.au/scholar_url?url=http://www.researchgate.net/profile/Ren_Hirayama/publication/256198221_Phylogenetic_systematics_of_chelonioid_sea_turtles/links/00463521fa2ee9f83c000000.pdf&hl=en&sa=X&scisig=AAGBfm2tPzF_sdyAUSfbG_I5aFA3oZmt3w&nossl=1&oi=scholarr&ei=RsMcVbKME4Wl8AWIioKIBQ&ved=0CBsQgAMoADAA

NOAA, 2008, Nesdis, viewed 29/3/15, url:< http://www.ncdc.noaa.gov/paleo/ctl/100k.html>

Spotila J R, Reina R D, Steyermark A C, Plotkin P T, Paladino F V 2000, “Pacific leatherback turtles face extinction”, nature, vol.405, pp.529-530, doi:10.1038/35014729

Tapilatu R F, Dutton P H, Tiwari M, Wibbels T, Ferinandus H V, Iwanginn W G, Nugroho B H 2013, “long-term decline of the western pacific leatherback, Dermochelyscoriacea: a globally important sea turtle population”, Ecological society of America, vol. 4, no. 2, doi:http://dx.doi.org/10.1890/ES12-00348.1

Valenzuela N 2008, ‘Relic thermosensitive gene expression in a turtle with genotypic sex determination’, Evolution, vol.62, no. 1, pp. 234-40, viewed 29/3/15, url:< http://onlinelibrary.wiley.com/doi/10.1002/jez.1402600117/abstract>

Valenzuela N, Badenhorst D, Montiel EE, Literman R 2014, ‘Molecular cytogenetic search for cryptic sex chromosomes in painted turtles Chrysemys picta’, Cytogentic genome research, vol. 144, no.1, pp.39-46, doi: 10.1159/000366076

Weishampel J F, Bagley D A, Ehrhart L M 2008,  “Earlier nesting by loggerhead sea turtles following sea surface warming”, Global change biology, vol. 10, no. 8, pp.1424-1427, doi:DOI: 10.1111/j.1529-8817.2003.00817.x

Images:

Anonymous 2013, Northern travel Ltd,viewed 29/3/15, https://cyprusnorth.wordpress.com/2013/06/25/the-caretta-caretta-turtle/

Freund J 2015, wwf, viewed 29/3/15, https://www.worldwildlife.org/species/hawksbill-turtle

Harasti 2015, NSW government, viewed 29/3/15, http://www.mpa.nsw.gov.au/simp-explore.html

Hakim J 2011, Asian herp blogs, viewed 29/3/15, https://bangkokherps.wordpress.com/2011/10/23/black-marsh-turtle/

Leonard S S 2012, Five point Five, viewed 29/3/15, http://fivepointfive.org/making-a-difference-turtle-conservation/

Nature 2007, PBworks, http://seaturtles.pbworks.com/w/page/15571583/Olive%20ridley

Reinhold L 2014, Phys.org, viewed 29/3/15, http://phys.org/news/2013-12-threatened-flatback-sea-turtle-natator.html