Department of Land Resources and Environmental Sciences, Montana State University , Bozeman, MT , USA.
Department of Plant Sciences and Plant Pathology, Montana State University , Bozeman, MT , USA.
PeerJ. 2014 Mar 25;2:e314. doi: 10.7717/peerj.314. eCollection 2014.
Females of solitary, nest-provisioning bees have relatively low fecundity, but produce large eggs as part of their overall strategy of investing substantially in each offspring. In intraspecific comparisons of several species of solitary, nest-provisioning bees and wasps, the size of the mature eggs produced increases with female body size. We further examined oocyte size-body size correlations in the solitary bee Megachile rotundata (F.), an important crop pollinator. We hypothesized that larger females carry larger basal oocytes (i.e., those next in line to be oviposited) but that body size-oocyte size correlations would be absent soon after emergence, before their first eggs fully matured. Because egg production is likely affected by the quantity of stored lipids carried over from the bees' immature stages, we also tested the hypothesis that female body size is correlated with the body lipid content at adult emergence, the time during which oocyte growth accelerates. We found significant correlations of body size with oocyte size variables chosen to reflect: (1) the magnitude of the investment in the next egg to be laid (i.e., the length and volume of the basal oocyte) and (2) the longer term potential to produce mature oocytes (i.e., the summed lengths and volumes of the three largest oocytes in each female). Positive correlations existed throughout the nesting season, even during the first week following adult emergence. The ability to produce and carry larger oocytes may be linked to larger females starting the nesting season with greater lipid stores (which we document here) or to greater space within the abdomen of larger females. Compared to other species of solitary bees, M. rotundata appears to have (1) smaller oocytes than solitary nest-provisioning bees in general, (2) comparable oocyte sizes relative to congeners, and (3) larger oocytes than related brood parasitic megachilids.
独居、筑巢的蜜蜂的雌性产卵量相对较低，但会产大卵，这是它们大量投资每个后代的整体策略的一部分。在几种独居、筑巢的蜜蜂和胡蜂的种内比较中，成熟卵的大小随着雌性体型的增大而增大。我们进一步研究了独居蜜蜂大切叶蜂（Megachile rotundata（F.））的卵母细胞大小与体型的关系，大切叶蜂是一种重要的作物传粉者。我们假设体型较大的雌性携带较大的基础卵母细胞（即即将产卵的那些），但在它们的第一批卵完全成熟之前，即刚从蛹期羽化出来后不久，体型与卵母细胞大小之间的相关性就会消失。因为产卵可能受到从蜜蜂未成熟阶段携带的储存脂质数量的影响，我们还测试了一个假设，即雌性体型与成虫羽化时的体脂含量（卵母细胞生长加速的时期）相关。我们发现，体型与卵母细胞大小变量之间存在显著的相关性，这些变量选择来反映：（1）即将产下的下一个卵的投资大小（即基础卵母细胞的长度和体积）和（2）产生成熟卵的长期潜力（即每个雌性中最大的三个卵母细胞的总长度和体积）。这种正相关性贯穿整个筑巢季节，甚至在成虫羽化后的第一周也存在。能够产生和携带更大的卵母细胞可能与较大的雌性在开始筑巢季节时具有更大的脂质储备（我们在这里记录了这一点）或较大的雌性腹部内的空间有关。与其他独居蜜蜂物种相比，大切叶蜂（Megachile rotundata）似乎具有：（1）比一般的独居筑巢蜜蜂更小的卵母细胞，（2）与同属种相比，卵母细胞大小相当，以及（3）比相关的寄生大切叶蜂具有更大的卵母细胞。
