Climate change resilience of a globally important sea turtle nesting population

Few studies have looked into climate change resilience of populations of wild animals. We use a model higher vertebrate, the green sea turtle, as its life history is fundamentally affected by climatic conditions, including temperature‐dependent sex determination and obligate use of beaches subject to sea level rise (SLR). We use empirical data from a globally important population in West Africa to assess resistance to climate change within a quantitative framework. We project 200 years of primary sex ratios (1900–2100) and create a digital elevation model of the nesting beach to estimate impacts of projected SLR. Primary sex ratio is currently almost balanced, with 52% of hatchlings produced being female. Under IPCC models, we predict: (a) an increase in the proportion of females by 2100 to 76%–93%, but cooler temperatures, both at the end of the nesting season and in shaded areas, will guarantee male hatchling production; (b) IPCC SLR scenarios will lead to 33.4%–43.0% loss of the current nesting area; (c) climate change will contribute to population growth through population feminization, with 32%–64% more nesting females expected by 2120; (d) as incubation temperatures approach lethal levels, however, the population will cease growing and start to decline. Taken together with other factors (degree of foraging plasticity, rookery size and trajectory, and prevailing threats), this nesting population should resist climate change until 2100, and the availability of spatial and temporal microrefugia indicates potential for resilience to predicted impacts, through the evolution of nest site selection or changes in nesting phenology. This represents the most comprehensive assessment to date of climate change resilience of a marine reptile using the most up‐to‐date IPCC models, appraising the impacts of temperature and SLR, integrated with additional ecological and demographic parameters. We suggest this as a framework for other populations, species and taxa.     

Classification and nomenclature of endogenous retroviral sequences (ERVs): Problems and recommendations

The genomes of many species are crowded with repetitive mobile sequences. In the case of endogenous retroviruses (ERVs) there is, for various reasons, considerable confusion regarding names assigned to families/groups of ERVs as well as individual ERV loci. Human ERVs have been studied in greater detail, and naming of HERVs in the scientific literature is somewhat confusing not just to the outsider. Without guidelines, confusion for ERVs in other species will also probably increase if those ERVs are studied in greater detail. Based on previous experience, this review highlights some of the problems when naming and classifying ERVs, and provides some guidance for detecting and characterizing ERV sequences. Because of the close relationship between ERVs and exogenous retroviruses (XRVs) it is reasonable to reconcile their classification with that of XRVs. We here argue that classification should be based on a combination of similarity, structural features, (inferred) function, and previous nomenclature. Because the RepBase system is widely employed in genome annotation, RepBase designations should be considered in further taxonomic efforts. To lay a foundation for a phylogenetically based taxonomy, further analyses of ERVs in many hosts are needed. A dedicated, permanent, international consortium would best be suited to integrate and communicate our current and future knowledge on repetitive, mobile elements in general to the scientific community.     

Swimming performance of hatchling green turtles is affected by incubation temperature

In an experiment repeated for two separate years, incubation temperature was found to affect the body size and swimming performance of hatchling green turtles (Chelonia mydas). In the first year, hatchlings from eggs incubated at 26°C were larger in size than hatchlings from 28 and 30°C, whilst in the second year hatchlings from 25.5°C were similar in size to hatchings from 30°C. Clutch of origin influenced the size of hatchlings at all incubation temperatures even when differences in egg size were taken into account. In laboratory measurements of swimming performance, in seawater at 28°C, hatchlings from eggs incubated at 25.5 and 26°C had a lower stroke rate frequency and lower force output than hatchlings from 28 and 30°C. These differences appeared to be caused by the muscles of hatchlings from cooler temperatures fatiguing at a faster rate. Clutch of origin did not influence swimming performance. This finding that hatchling males incubated at lower temperature had reduced swimming ability may affect their survival whilst running the gauntlet of predators in shallow near-shore waters, prior to reaching the relative safety of the open sea.     

Sex‐specific survival to maturity and the evolution of environmental sex determination

Four decades ago, it was proposed that environmental sex determination (ESD) evolves when individual fitness depends on the environment in a sex‐specific fashion—a form of condition‐dependent sex allocation. Many biological processes have been hypothesized to drive this sex asymmetry, yet a general explanation for the evolution of sex‐determining mechanisms remains elusive. Here, we develop a mathematical model for a novel hypothesis of the evolution of ESD, and provide a first empirical test using data across turtles. ESD is favored when the sex‐determining environment affects annual survival rates equivalently in males and females, and males and females mature at different ages. We compare this hypothesis to alternative hypotheses, and demonstrate how it captures a crucially different process. This maturation process arises naturally from common life histories and applies more broadly to condition‐dependent sex allocation. Therefore, it has widespread implications for animal taxa. Across turtle species, ESD is associated with greater sex differences in the age at maturity compared to species without ESD, as predicted by our hypothesis. However, the effect is not statistically significant and will require expanded empirical investigation. Given variation among taxa in sex‐specific age at maturity, our survival‐to‐maturity hypothesis may capture common selective forces on sex‐determining mechanisms.     

A swimy locus on Y chromosome of the platyfish (Xiphophorus maculatus) is derived from a novel DNA transposon Zisupton

A swimy locus derived from a novel DNA transposon Zisupton was located on the sex determination region (SD) of Xiphophorus maculatus. The analysis of expression pattern showed that swimy was exclusively expressed in adult testis in X. maculatus. The putative 939 aa sequence contains four Zn-finger domains, such as two C2H2 type, one NFX type and one SWIM type Zn-finger domain, and one SAP DNA-binding domain. Swimy has about 7 copies per haploid X. maculatus genome with Y-specific copies located in the SD region, and become the second new W-linked marker of platyfish. Analysis of the structure and distribution of this sex-linked marker is benefit to shed new light on the evolutionary dynamics of sex chromosomes in fish.     

Sox9在温度依赖型性别决定中的功能初探

在一些爬行动物中,个体的性别完全取决于胚胎发育过程中的环境温度,称之为温度依赖型性别决定(temperaturedependent sex determination,TSD).TSD的分子机制长期是个谜,特别是调控早期性腺分化的分子基础仍不清楚.本文通过表达分析和基因敲低手段研究了Sox9基因在红耳龟雄性性腺分化中的生物学功能,为TSD动物的性别决定和性腺发育的分子机制的研究奠定了基础.qRT-PCR显示,从性腺分化前的17期起,Sox9呈现产雄温度(male-producing temperature,MPT)性腺特异性高表达,而在产雌温度(female-producing temperature,FPT)性腺中表达水平极低.免疫组化进一步证实了SOX9蛋白的MPT特异性表达趋势,其定位于Sertoli前体细胞核中.温度置换实验显示,与MPT性腺相比,MPT→FPT性腺中(16期置换)的Sox9表达量从17期起就显著降低,表明Sox9能快速响应温度变化.同时MPT性腺经过雌激素处理后,Sox9表达量亦快速下调.功能缺失研究显示,经过Sox9-RNAi处理后,90.9%(20/22)的MPT性腺结构明显雌性化,皮质区高度发育,髓质区退化,揭示Sox9的敲低能导致雄性向雌性性逆转.上述研究表明,Sox9是红耳龟早期睾丸分化的关键调控因子,参与TSD的雄性分化通路.     

Low temperature has opposite effects on sex determination in a marine fish at the larval/postlarval and juvenile stages

Temperature‐dependent sex determination (TSD) can be observed in multiple reptile and fish species. It is adaptive when varying environmental conditions advantage either males or females. A good knowledge of the thermosensitive period is key to understand how environmental changes may lead to changes in population sex ratio. Here, by manipulating temperature during development, we confirm that cold temperature (16°C) increases the proportion of fish that develop as females in European sea bass (Dicentrarchus labrax) until 56 days posthatching, but show that it has an opposite effect at later stages, with the proportion of males reaching ~90% after 230 days at 16°C. This is the first observation of opposite effects of temperature at different time periods on the sex ratio of a vertebrate. Our results highlight the potential complexity of environmental effects on sex determination.