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SEX RATIO SELECTION AND THE EVOLUTION OF ENVIRONMENTAL SEX DETERMINATION IN LABORATORY POPULATIONS OF MENIDIA MENIDIA
Author(s) -
Conover David O.,
Van Voorhees David A.,
Ehtisham Amir
Publication year - 1992
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1992.tb01164.x
Subject(s) - biology , sex ratio , population , operational sex ratio , selection (genetic algorithm) , ecology , fish <actinopterygii> , zoology , demography , fishery , artificial intelligence , sociology , computer science
What happens when a population with environmental sex determination (ESD) experiences a change to an extreme environment that causes a highly unbalanced sex ratio? Theory predicts that frequency‐dependent selection would increase the proportion of the minority sex and decrease the level of ESD in subsequent generations. We empirically modeled this process by maintaining five laboratory populations of a fish with temperature‐dependent sex determination (the Atlantic silverside, Menidia menidia ) in extreme constant temperature environments that caused highly skewed sex ratios to occur initially. Increases in the minority sex consistently occurred from one generation to the next across all five populations, first establishing and then maintaining a balanced sex ratio until termination of the experiment at 8 to 10 generations. The extent to which the level of ESD changed as balanced sex ratios evolved, however, was not consistent. Two populations that experienced high temperatures each generation displayed a loss of ESD, and in one of these ESD was virtually eliminated. This suggests that temperature‐insensitive, sex‐determining genes were being selected. In populations maintained in low temperature environments, however, the level of ESD did not decline. Instead, the response of sex ratio to temperature was adjusted upward or downward, perhaps by selection of sex‐determining genes sensitive to higher (or lower) temperatures. The two different outcomes at low versus high temperatures occurred independent of the geographic origin of the founding population. Our results demonstrate that ESD is capable of evolving in response to selection.