Breeding periodicity for male sea turtles, operational sex ratios, and implications in the face of climate change

Species that have temperature-dependent sex determination (TSD) often produce highly skewed offspring sex ratios contrary to long-standing theoretical predictions. This ecological enigma has provoked concern that climate change may induce the production of single-sex generations and hence lead to population extirpation. All species of sea turtles exhibit TSD, many are already endangered, and most already produce sex ratios skewed to the sex produced at warmer temperatures (females). We tracked male loggerhead turtles (Caretta caretta) from Zakynthos, Greece, throughout the entire interval between successive breeding seasons and identified individuals on their breeding grounds, using photoidentification, to determine breeding periodicity and operational sex ratios. Males returned to breed at least twice as frequently as females. We estimated that the hatchling sex ratio of 70:30 female to male for this rookery will translate into an overall operational sex ratio (OSR) (i.e., ratio of total number of males vs females breeding each year) of close to 50:50 female to male. We followed three male turtles for between 10 and 12 months during which time they all traveled back to the breeding grounds. Flipper tagging revealed the proportion of females returning to nest after intervals of 1, 2, 3, and 4 years were 0.21, 0.38, 0.29, and 0.12, respectively (mean interval 2.3 years). A further nine male turtles were tracked for short periods to determine their departure date from the breeding grounds. These departure dates were combined with a photoidentification data set of 165 individuals identified on in-water transect surveys at the start of the breeding season to develop a statistical model of the population dynamics. This model produced a maximum likelihood estimate that males visit the breeding site 2.6 times more often than females (95%CI 2.1, 3.1), which was consistent with the data from satellite tracking and flipper tagging. Increased frequency of male breeding will help ameliorate female-biased hatchling sex ratios. Combined with the ability of males to fertilize the eggs of many females and for females to store sperm to fertilize many clutches, our results imply that effects of climate change on the viability of sea turtle populations are likely to be less acute than previously suspected.

Retracted: Experimental evidence that maternal corticosterone controls adaptive offspring sex ratios

1. Sex allocation theory has received considerable attention, yet the mechanism(s) by which mothers skew offspring sex ratios remain unknown. In birds, females are the heterogametic sex, which potentially gives them control of whether gametes will be male or female. How females might control the sex of the gamete is unclear, but one possibility is that variation in steroid hormones may mediate this process. 2. We experimentally altered circulating levels of corticosterone in female Gouldian finches (Erythrura gouldiae), a species that demonstrates both extreme stress responses and extreme offspring sex ratio biases when breeding with a low-quality (genetically incompatible) partner. 3. During egg production, individual females received both corticosterone and metyrapone (a corticosterone-synthesis inhibitor) implants, in random order, to induce both high and low levels of circulating stress hormones (within physiological limits). 4. We found that females with elevated corticosterone levels produced male-biased sex ratios, but when the same females were treated with metyrapone they produced female-biased offspring sex ratios. 5. These stress responses are adaptive because females constrained to breeding with low-quality males can substantially increase their fitness by overproducing sons. Changes in maternal corticosterone levels during stressful situations, such as the quality of a breeding partner, may provide an endocrine mechanism that can be exploited for strategic sex allocation.

Using hospital standardised mortality ratios to assess quality of care--proceed with extreme caution

Australian Health Ministers have endorsed the hospital standardised mortality ratio (HSMR) as a key indicator of quality and safety, and efforts are currently underway towards its national implementation. In the United Kingdom, Canada, the Netherlands and the United States, the HSMR has been used for several years within organisations to monitor performance and response to various quality and safety programs. In the UK and Canada, the HSMR is also publicly reported and used to compare performance between hospitals. The validity and reliability of the HSMR as a screening tool for distinguishing low-quality from high-quality hospitals remain in doubt, and it has not yet been proven that HSMR reporting necessarily leads to worthwhile improvement in quality of care and patient outcomes.

The relationship between carbon stable isotope ratios of hatchling down and egg yolk in Black-headed Gulls

We reconstructed the nutrient source for egg synthesis by sampling Black-headed Gull (Larus ridibundus) eggs for yolk, analyzing their carbon stable isotope ratio, and comparing that to hatchling down. Most of the variation in carbon stable isotope ratio was explained by differences between nests, the within-nest variation being explained by laying order. These data indicate significant differences in diet choice between individual females and changes in food choice or body-store dynamics during egg laying. Among-egg variation in the carbon stable isotope ratios of the yolk were closely reflected in the hatchling down, on average down being enriched by 3.1‰ δ13C relative to yolk. Our findings support the contention that pre-laying female diets can be evaluated from hatchling down.

Effects of diet change on carbon and nitrogen stable-isotope ratios in blood cells and plasma of the long-nosed bandicoot (Perameles nasuta)

Carbon (C) and nitrogen (N) stable isotopes offer a powerful tool for assessing the extent of tissue assimilation of dietary components. However, the method relies on knowledge of diet-tissue isotopic discrimination and how quickly diet shifts become apparent in various tissues. In the present study, blood plasma and blood cells, tissues that are easily obtained under field conditions, were used to validate the stable isotope method over a period of 4-5 weeks using captive long-nosed bandicoots (Perameles nasuta). Diet-tissue discrimination effects appeared to be small. For C, derived diet-tissue isotopic discriminations were 1.4‰ for blood plasma and -0.2‰ for blood cells. For N the values were 2.8‰ and 2.1‰, respectively, and were independent of the nitrogen content of the food. C and N turnover measurements in the blood plasma and cells of the bandicoots indicated that blood plasma provides dietary information integrated over a period of ∼3 weeks, whereas blood cells give an impression of the assimilated diet over a period of as much as half a year. These turnover rates were low compared with the little information available for birds and eutherian mammals, and probably relate to the typically low metabolic rate of marsupials.

Geographical variation and population structure in the White-rumped Sandpiper Calidris fuscicollis as shown by morphology, mitochondrial DNA and carbon isotope ratios

We studied the population structure of a high arctic breeding wader bird species, the White-rumped Sandpiper Calidris fuscicollis. Breeding adults, chicks and juveniles were sampled at seven localities throughout the species' breeding range in arctic Canada in 1999. The mitochondrial control region was analysed by DNA sequencing, feathers were analysed for carbon isotope ratios (C13/C12) by isotope ratio mass spectrometry, and morphological measurements were analysed using principal component analyses, taking the effect of sex into account (identified by molecular genetic methods). In general, our results support the notion that the White-rumped Sandpiper is a monotypic species with no subspecies, and most of the morphological and genetic variation occurs within sites. Nevertheless, some differences between sites were found. Birds from the two northernmost sites (Ellesmere and Devon Islands) had relatively longer bill and wing and shorter tarsus than birds sampled further south, possibly reflecting genetic differences between populations. The carbon isotope ratios were higher at the easternmost site (Baffin Island), revealing differences in the isotope content of the food. The mtDNA sequences showed no significant differentiation between sites and no pattern of isolation-by-distance was found. Based on the mtDNA variation, the species was estimated to have a long-term effective population size of approximately 9,000 females. The species shows no clear evidence of any population expansion or decline. Our results indicate that carbon isotope ratios, and possibly also certain mtDNA haplotypes, may be useful as tools for identifying the breeding origin of White-rumped Sandpipers on migration and wintering sites.