The Turtle & the Octopus

Hapalochlaena sp. from New South Wales. Photo

Credit: David Brenemen

Moreton Bay in Queensland, Australia is estimated to support 20,000 sea turtles. The bay has extensive seagrass beds used as feeding areas by the green sea turtle, (Chelonia mydas). The seagrass beds also provide habitat for many marine creatures, including the blue-lined octopus, Hapalochlaena fasciata, a visually cryptic species that hides in tide pools by blending with its surroundings using pigmented chromatophores. When threatened, the octopus displays bright blue rings and lines, which act as a warning to potential predators. The blue-lined octopus delivers the neurotoxic tetrodotoxin (TTX) when it bites, a molelcule that has been hypothesized to be used for defense although evidence to support this has been absent. Two dead adult green sea turtles were recently found in Moreton Bay, despite the outward appearance of being healthy, the turtles showed no life threatening injuries. Upon dissection both turtles appeared normal, their digestive tracts contained large quantities of the seagrass (Halophila ovalis) and inspection of the contents revealed a bluelined octopus encased within a seagrass bolus in each of the two turtles. In both cases esophageal tissue directly around the octopus was red and inflamed suggesting the turtles had been envenomation, further tests on the turtles' tissues confirmed TTX poisoning. This case provides the first evidence of the octopus using TTX as a possible defense mechanism, and is the first evidence to suggest that this small octopus is a hazard to turtles.

CitationKathy A. Townsend, Jens Altvater, Michael C. Thomas, Qamar A. Schuyler and Geoffrey W. Nette. 2012. Death in the octopus’ garden: fatal blue-lined octopus envenomations of adult green sea turtles. Marine Biology 159, 689-695

Multiple Paternity, Green Turtles, & Climate Change

A hatching Green Turtle. Photo credit:
 Kimberly Stokes, University of Exetar.

The mating habits of marine turtle may help protect them against the effects of climate change, according to new research led by the University.

Published yesterday (25 January 2012) in the Proceedings of the Royal Society B, the study shows how mating patterns of a population of endangered green turtles may be helping them deal with the fact that global warming is leading to a disproportionate number of females being born.

The gender of baby turtles is determined by the temperature of the eggs during incubation, with warmer temperatures leading to more females being born. Higher average global temperatures mean that offspring from some populations are predominantly female. This is threatening the future of some populations and there are concerns that inbreeding within groups due to a lack of males will lead to health problems.

The study focused on a population of the green turtle, Chelonia mydas, nesting in Northern Cyprus, where, due to the high summer temperatures, 95 per cent of babies are female. The study involved a team from the University of Exeter (UK), University of Lefke (Turkey) and North Cyprus Society for Protection of Turtles. Through DNA testing, they were able to ascertain the paternity of baby turtles and, contrary to what they had expected, they found a large number of mating males.

The researchers found that 28 males sired offspring with 20 nesting females: an average of 1.4 males for every female. This means that each female’s offspring were sired by one or more fathers. The researchers were surprised to find no evidence that any males fathered offspring born in that season with more than one female.

The Cornwall Campus-based research team had thought that one single male might be breeding with multiple females. However, their results suggest that a large number of males are mating with different females at different times. This means that there is less chance of inbreeding.

The team also carried out satellite tracking to discover that males cover thousands of miles of ocean within one breeding season. This suggests they could have also been mating with females at other sites in Turkey or North Africa.

Lead researcher University of Exeter Biosciences PhD student Lucy Wright said: “It is fantastic to know that there are so many males fathering offspring in this population of green turtles. There is great concern that a lack of males could lead to inbreeding in small populations of marine turtles, potentially causing a population crash. However our research suggests that there are more males out there than expected considering the female-biased hatchling sex ratios and that their mating patterns will buffer the population against any potential feminising effects of climate change.”

Corresponding author Dr Annette Broderick added: “Climate change remains a great threat to marine turtles, but our ongoing research will help us focus on where the priority areas are for management that may help them cope with future change.”

The work was funded by a NERC studentship with additional support from NERC Biomolecular Analysis Facility, Sheffield.

Citation
L. I. Wright, K. L. Stokes, W. J. Fuller, B. J. Godley, A. McGowan, R. Snape, T. Tregenza, & A. C. Broderick. Turtle mating patterns buffer against disruptive effects of climate change. Proceedings of the Royal Society B: Biological Sciences, 2012; DOI: 10.1098/rspb.2011.2285