Anisogamy does not always promote the evolution of mating competition traits in males

Anisogamy has evolved in most sexually reproducing multicellular organisms allowing the definition of the male and female sexes, producing small and large gametes. Anisogamy, as the initial sexual dimorphism, is a good starting point to understand the evolution of further sexual dimorphisms. For instance, it is generally accepted that anisogamy sets the stage for more intense mating competition in males than in females. We argue that this idea stems from a restrictive assumption on the conditions under which anisogamy evolved in the first place: the absence of sperm limitation (assuming that all female gametes are fertilized). Here, we relax this assumption and present a model that considers the coevolution of gamete size with a mating competition trait, starting in a population without dimorphism. We vary gamete density to produce different scenarios of gamete limitation. We show that, while at high gamete density the evolution of anisogamy always results in male investment in competit...配子异型（anisogamy）已在绝大多数进行有性繁殖的多细胞生物中演化形成，借此可定义产生小型配子与大型配子的雄性与雌性性别。作为初始的性别二态性形式，配子异型是理解后续更深层次性别二态性演化的绝佳切入点。例如，学界普遍认为，配子异型为雄性带来了较雌性更为激烈的交配竞争奠定了基础。我们提出，这一观点源自对配子异型初始演化条件的限制性假设：不存在精子限制（即假定所有雌性配子均可完成受精）。本研究放宽了这一假设，构建了一个模型，该模型考虑了在无性别二态性的种群中，配子大小与交配竞争性状的协同演化过程。我们通过调整配子密度以模拟不同的配子限制场景。研究结果表明，在配子密度较高的情况下，配子异型的演化总会促使雄性在竞争...