Indeed, given that multiple ‘clonal’ strains of extant mangrove killifish clearly have escaped the perils of intense inbreeding, at least over the short term, this androdioecious species with a mixed-mating system presumably GSK458 price enjoys some of the best of two worlds: outcrossing’s long-term as well as short-term advantages (continued genetic health and adaptability through recombination), and selfing’s immediate benefits (fertilization assurance and perhaps the intact propagation of locally adapted genotypes). Especially for animals that are sequential
hermaphrodites, the most powerful evolutionary explanations for the ontogeny of sex change have come from a branch of
sex-allocation theory known as the size-advantage hypothesis or SAH (Ghiselin, 1969; Warner, 1975, 1988), which basically predicts that sex change is favored by natural selection when an individual reproduces most effectively as one sex GSK3235025 price when small (and young) but as the other sex when larger (and older). Depending on the biology and ecology of a particular species, males might have a reproductive advantage when small and females when large, in which case protandry would be selectively favored; but in other species, females might reproduce better when small and males when large, in which case protogyny might tend to evolve. The empirical challenge has been to understand what biological conditions generally tip the scales in favor of individuals reproducing as dams versus sires at various size cohorts or age classes. For sequentially hermaphroditic fishes and invertebrates alike, SAH has made predictions about patterns of sex change that seem to be consistent with many observational and experimental tests. Because humans are mammals MCE公司 with sexual reproduction, people are familiar with the concept of pregnancy, that is with the otherwise outlandish notion that one individual carries a genetically different individual inside its body for an extended period of
time before expelling the latter through an orifice. If you are a man, you might feel relieved that this weighty reproductive imposition has been delegated to females in Homo sapiens; and if you are a woman, the thought of becoming pregnant might elicit any of a gamut of emotions ranging from joy to fear or loathing, depending on the circumstances. One day when I was about 8 years old, I had an insight: God had arranged things equitably for men and women. A man could anticipate being drafted into 2 years of military combat whereas a woman might spend on average about 2 years of life in a state of pregnancy (which I imagined to be an equally unpleasant sentence). This childhood revelation is silly, but in some ways it was prescient.