Nutrition affects larval survival and the development of morphological traits in male and female flour beetles, but genital size and shape remain canalized

The caloric content and macronutrient ratio of the diet consumed is a
major source of phenotypic variation in most animal populations. While
these nutritional effects have been well-documented for a variety of
life-history and morphological traits, the effects of nutrition on male
genitals are poorly understood but genitals are thought to be more
canalised than general morphology and hence less susceptible to variation
in nutrition. Even less is known about the effects of nutrition on female
genital form, which to our knowledge, have never been investigated. Here
we tested for the effects of juvenile dietary macronutrients (protein and
carbohydrate) on larval survival, and adult morphology, including genital
size and shape in male and female flour beetles (Tribolium castaneum). We
found there was nutritionally induced plasticity in larval survival and
morphology, although the latter effect was variable, with body size being
most responsive to dietary macronutrients and genital size and shape being
least responsive. Functionally equivalent morphological traits in the
sexes responded similarly to nutrition. Previously, we showed that the
genitalia of male and female T. castaneum are subject to strong
stabilizing sexual selection, and our current findings suggest that
developmental mechanisms reduce the nutritional sensitivity of male and
female genitals, possibly to ensure matching during mating.

饮食的热量含量与宏量营养素比例，是多数动物种群表型变异的主要来源。尽管这类营养效应对多种生活史与形态性状的影响已被充分证实，但营养对雄性生殖器的作用却鲜有研究；不过学界普遍认为，生殖器相较于一般形态结构具有更强的发育稳态性，因此受营养变异的影响更小。关于营养对雌性生殖器形态的影响，相关认知则更为匮乏，据我们所知，目前尚无相关探究。本研究以赤拟谷盗（Tribolium castaneum）为实验对象，探究了幼年期饮食宏量营养素（蛋白质与碳水化合物）对幼虫存活率以及成虫形态（包括雌雄个体生殖器的大小与形态）的影响。研究发现，幼虫存活率与成虫形态均存在营养诱导的表型可塑性；不过成虫形态的营养响应存在差异：躯体大小对饮食宏量营养素的响应最为显著，而生殖器的大小与形态响应最弱。两性中功能等效的形态性状，其营养响应模式基本一致。此前我们的研究已证实，赤拟谷盗雌雄生殖器均受到强烈的稳定化性选择作用；而本研究结果表明，发育机制会降低雌雄生殖器对营养的敏感性，这可能是为了保障交配过程中两性生殖器的匹配适配。