Department of Biological Sciences, National University of Singapore, Singapore.
Department of Evolutionary Biology & Environmental Studies, University of Zürich-Irchel, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
Proc Biol Sci. 2023 May 10;290(1998):20222531. doi: 10.1098/rspb.2022.2531. Epub 2023 May 3.
Male sexual ornaments often evolve rapidly and are thought to be costly, thus contributing to sexual size dimorphism. However, little is known about their developmental costs, and even less about costs associated with structural complexity. Here, we quantified the size and complexity of three morphologically elaborate sexually dimorphic male ornaments that starkly differ across sepsid fly species (Diptera: Sepsidae): (i) male forelegs range from being unmodified, like in most females, to being adorned with spines and large cuticular protrusions; (ii) the fourth abdominal sternites are either unmodified or are converted into complex appendages; and (iii) male genital claspers range from small and simple to large and complex (e.g. bifurcated). We tracked the development of 18 sepsid species from egg to adult to determine larval feeding and pupal metamorphosis times of both sexes. We then statistically explored whether pupal and adult body size, ornament size and/or ornament complexity are correlated with sex-specific development times. Larval growth and foraging periods of male and female larvae did not differ, but the time spent in the pupal stage was 5% longer for sepsid males despite emerging 9% smaller than females on average. Surprisingly, we found no evidence that sexual trait complexity prolongs pupal development beyond some effects of trait size. Evolving more complex traits thus does not incur developmental costs at least in this system.
雄性性装饰品通常进化迅速，被认为是有代价的，因此有助于性大小二型。然而，人们对它们的发育代价知之甚少，甚至对与结构复杂性相关的代价知之甚少。在这里，我们量化了三种形态复杂的雄性性二型性装饰物的大小和复杂性，这些装饰物在 sepsid 蝇种（双翅目：Sepsidae）中差异明显：（i）雄性前腿从像大多数雌性那样未修饰，到装饰有刺和大的表皮突起；（ii）第四腹节胸板要么未修饰，要么转化为复杂的附属物；（iii）雄性生殖器夹钳从小而简单到大而复杂（例如分叉）。我们跟踪了 18 种 sepsid 物种从卵到成虫的发育，以确定两性的幼虫取食和蛹变态时间。然后，我们从统计学上探讨了蛹和成虫体型、装饰品大小和/或装饰品复杂性是否与性别特异性发育时间相关。雄性和雌性幼虫的幼虫生长和觅食期没有差异，但雄性蛹期的时间比雌性长 5%，尽管平均而言，雄性蛹期比雌性蛹期小 9%。令人惊讶的是，我们没有发现证据表明性特征复杂性会使蛹发育延长到特征大小之外的某些影响。因此，在这个系统中，进化更复杂的特征至少不会带来发育代价。
