Yamaguchi Sachi
Department of Information Systems Creation, Faculty of Engineering, Kanagawa University, Yokohama 221-8686, Japan.
J Theor Biol. 2016 Oct 21;407:339-348. doi: 10.1016/j.jtbi.2016.07.012. Epub 2016 Jul 12.
Bidirectional sex change is observed in many teleost fish. When social conditions change, the sex transition may take place over a period of several days to a few months. To understand temporal differences for sex change in either direction, I propose a simple mathematical model for the hormone-enzyme dynamics. Aromatase (P450arom) catalyses the synthesis of estradiol from testosterone. I assume that a change in social conditions for individuals affects the rates of production and degradation of P450arom. I then consider the evolution of parameters in the dynamics. Optimal parameter values are those that minimize total fitness cost, defined as the sum of fitness losses due to delay in being a functional male or female, and the cost of accelerated degradation of P450arom in changing from female to male sex. The model predicts that, in haremic species, sex change promotes a faster degradation of P450arom, resulting in a faster female-to-male transition than male-to-female transition. In contrast, in monogamous species, or with a small number of females, there is no benefit in a faster degradation of P450arom when changing to male, resulting in approximately equal timespans for sex change in either direction.
在许多硬骨鱼类中都观察到了双向性转变。当社会条件发生变化时，性别转变可能会在几天到几个月的时间内发生。为了了解双向性别转变的时间差异，我提出了一个关于激素 - 酶动力学的简单数学模型。芳香化酶（P450arom）催化睾酮合成雌二醇。我假设个体社会条件的变化会影响P450arom的产生和降解速率。然后我考虑动力学中参数的演变。最优参数值是那些使总适应度成本最小化的参数值，总适应度成本定义为因延迟成为功能性雄性或雌性而导致的适应度损失，以及在从雌性转变为雄性时P450arom加速降解的成本之和。该模型预测，在一雄多雌制物种中，性别转变会促进P450arom更快地降解，导致从雌性到雄性的转变比从雄性到雌性的转变更快。相比之下，在一夫一妻制物种中，或者雌性数量较少的情况下，转变为雄性时更快地降解P450arom没有好处，导致双向性别转变的时间跨度大致相等。
