Squamate hatchling size and the evolutionary causes of negative offspring size allometry

Although fecundity selection is ubiquitous, in an overwhelming majority of animal lineages, small species produce smaller number of offspring per clutch. In this context, egg, hatchling and neonate sizes are absolutely larger, but smaller relative to adult body size in larger species. The evolutionary causes of this widespread phenomenon are not fully explored. The negative offspring size allometry can result from processes limiting maximal egg/offspring size forcing larger species to produce relatively smaller offspring (‘upper limit’), or from a limit on minimal egg/offspring size forcing smaller species to produce relatively larger offspring (‘lower limit’). Several reptile lineages have invariant clutch sizes, where females always lay either one or two eggs per clutch. These lineages offer an interesting perspective on the general evolutionary forces driving negative offspring size allometry, because an important selective factor, fecundity selection in a single clutch, is eliminate...尽管繁殖力选择（fecundity selection）普遍存在，但在绝大多数动物类群中，体型较小的物种每窝产下的后代数量反而更少。在此背景下，体型较大的物种，其卵、孵出幼体与新生幼体的绝对尺寸更大，但相对于成体体型的比例却更小。这一普遍现象的进化成因尚未完全阐明。这种后代大小负异速生长（negative offspring size allometry）可能源于两类过程：一类是限制最大卵/后代尺寸的机制，迫使大物种产生相对更小的后代（即"上限限制"）；另一类是限制最小卵/后代尺寸的机制，迫使小物种产生相对更大的后代（即"下限限制"）。部分爬行类群具有固定的窝卵数，雌性每窝仅产1枚或2枚卵。此类类群为探究驱动后代大小负异速生长的通用进化力量提供了有趣的研究视角，因为一项关键的选择因子——单窝繁殖力选择——已被消除...