In the nematode Mermis nigrescens, sex is determined by the size of the grasshopper host in which an individual nematode develops Craig and Webster ; in the echiurid worm Bonellia viridis, sex is determined by whether a larva settles on the seafloor or on a female conspecific Baltzer Here, we focus on traits associated with temperature-dependent sex determination TSD , a classic polyphenism, in a model turtle species to address the evolutionary potential of species with TSD to respond to rapid climate change. Finally, a few species including the snapping turtle Chelydra serpentina , crocodilians e. For example, what traits might be most affected by anthropogenic environmental change? TSD occurs in some fish e. Photoperiod determines sex in the saltbush Atriplex halimus Talamali et al. The most widespread mode of ESD is temperature-dependent sex determination TSD , in which the sex of offspring is determined by temperatures experienced by the developing embryo during egg incubation Bull Unlike genotypic sex determination, in which sex is determined at fertilization by the complement of sex chromosomes present in the zygote, no sex chromosomes are present in species with ESD; instead sex is determined by some environmental cue during a discrete period later in embryonic development Wibbels et al.
The most widespread mode of ESD is temperature-dependent sex determination TSD , in which the sex of offspring is determined by temperatures experienced by the developing embryo during egg incubation Bull Finally, a few species including the snapping turtle Chelydra serpentina , crocodilians e. Within TSD, several different patterns of sex determination are present. Adaptive changes in allele frequency of heritable traits, in response to selective pressures, allow organisms to keep pace with changes in the environment. TSD occurs in some fish e. Photoperiod determines sex in the saltbush Atriplex halimus Talamali et al. Species that fail to adapt to the novel environmental conditions imposed by human activity may face extinction, and we as humans will be faced with a loss of biodiversity and the ecosystem services provided by that biodiversity. Environmental sex determination ESD is an ideal trait for assessing the evolutionary potential of organisms to respond to rapid environmental change. We show, first, that sex-ratio outcomes in species with TSD are sensitive to climatic variation. Can the most-impacted traits evolve in response to anthropogenic environmental change and, if so, can they respond quickly enough to keep pace with the rapid rate of such change? There is also mounting evidence that the effect of temperature fluctuation on hatchling phenotype, including sex, differs depending on whether such fluctuation occurs primarily around the upper or lower unisexual mean temperature Les et al. ESD occurs in a diverse range of taxa, with an impressive diversity in the environmental cues that determine sex. Such microevolutionary responses permit organisms to remain adapted to their environment even when current conditions differ from those experienced by their ancestors e. We find that these traits display different patterns of adaptive potential: Unlike genotypic sex determination, in which sex is determined at fertilization by the complement of sex chromosomes present in the zygote, no sex chromosomes are present in species with ESD; instead sex is determined by some environmental cue during a discrete period later in embryonic development Wibbels et al. For example, what traits might be most affected by anthropogenic environmental change? Therefore, the most likely response of species with TSD to anthropogenically induced climate change may be a combination of microevolution in thermal sensitivity of the sex-determining pathway and of plasticity in maternal nesting behavior. Type 1b TSD, which occurs in the tuatara Sphenodon punctatus , demonstrates the reverse pattern, with males produced at high incubation temperatures and females at low temperatures e. Currently, anthropogenically driven environmental changes are occurring orders of magnitude faster than they did prior to human influence, which could potentially outpace the ability of some organisms to adapt. The thermosensitive period, during which sex determination occurs, is generally the middle third of embryonic development Wibbels et al. Advanced Search Abstract Organisms become adapted to their environment by evolving through natural selection, a process that generally transpires over many generations. In particular, scientists are increasingly interested in assessing the evolutionary potential of organisms in the context of rapid environmental change Visser ; Lavergne et al. The focus of research on anthropogenic environmental change has begun to shift from compilations of the direct effects of rapid environmental change on organisms e. In species with Type 1a TSD, including most turtles such as red-eared sliders Trachemys scripta , females are produced at high incubation temperatures and males at low temperatures e. The pace at which evolution occurs has been the subject of intense study, and depends on several factors, including:
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