Sex determination is a fundamental process in all sexual organisms.
Many experiments detected that sex allocation should vary depending on the social environment into which offspring will emerge and the relative quality of male and female offspring that parents are likely to produce.*
Paul et al. have reported that environmental conditions also affect the sex ratio of malaria parasites.
Research found variability occurs between hosts within a population and during the course of single infections, which led to the suggestion that sex allocation might partially be a response to environmental conditions.*
Ludivine de Menten et al. compared the primary sex ratios laid by queens in monogynous and in polygynous experimental colonies of C. obscurior. The proportion of haploid eggs laid by queens was significantly lower in single-queen than in multiple-queen colonies. Furthermore, queens rapidly adjusted their primary sex ratios to changes in colony queen numbers, indicating that queens can make an adaptive response.*
Information about the environment is clearly important since females have to estimate the degree of LMC that will be experienced by their sons.
David M. Shuker et al. explored how information use influences the sex allocation behavior of the parasitoid wasp Nasonia vitripennis in response to local mate competition. Optimal sex ratios under local mate competition require females to estimate the number of other females that contribute eggs to a patch. Females rapidly changed their sex allocation in response to changes in the number of females in the environment, suggesting that they are not constrained by how quickly they can respond to new information.
Furthermore, females also showed some response to olfactory cues that indicated oviposition by other females, suggesting that such indirect cues may be part of their information repertoire.
David M. Shuker et al. concluded by highlighting variation among species in whether particular cues are used for sex allocation.*
Current studies indicate that female birds can detect offspring sex in the reproductive tract. Furthermore, females are capable of making decisions concerning investment in sons and daughters based on this information.*
Experimental studies of wild birds suggest that females have an ability to control the sex ratio of their offspring in response to variation in sex-specific fitness benefits. Birds and mammals with chromosomal sex determination have long been thought to be constrained in their sex allocation decisions by their means of sex determination. New genetic techniques for sex identification, and clever experimental manipulations of wild birds, have forced a reexamination of the constraint idea: female birds are apparently capable of quite precise adjustments of their offspring sex ratio.*
Facts suggest that male offspring will be more severely affected by limited nutrition than female offspring, and hence that breeding females in poorer conditions, which are known to produce less well-provisioned eggs, should be selected to bias sex allocation in favor of daughters.
Emily Willingham assessed red-eared slider turtle's mass, carapace width and length, and plastron length of hatchlings from three different incubation temperature regimes. Differences in incubation temperature affected mass in turtles of the same sex.*
David Crews et al. studied the phenomenon of temperature-dependent sex determination in reptiles. They illustrated how the experience of a particular temperature during a sensitive period of embryogenesis sculpts not only the patterns of expression of genes involved in sex determination and gonadal differentiation, but also the morphological, physiological, neuroendocrine, and behavioral traits of the adult phenotype.*
Depending upon the species, the pattern of TSD may be one in which females are produced at low incubation temperatures relative to the temperatures that produce males; males are produced at low temperatures relative to the temperatures that produce females; or females are produced at temperatures at either extreme with males being produced at intermediate temperatures.
David Crews et al. observed a different pattern of TSD in the leopard gecko (Eublepharis macularius), and found that high and low incubation temperatures produced only females whereas intermediate incubation temperatures produced different sex ratios. That is, extreme temperatures (26¡ãC and 34¡ãC) are female-producing incubation temperatures, whereas intermediate temperatures result in different sex ratios: 30¡ãC (Tf) produces a female-biased sex ratio (25:75) and 32.5¡ãC (Tm) a male-biased sex ratio (75:25).
* For further details, please refer to Deep Structure Studies 7: Experimental Reviews and References I.