某些隔膜物种(Sepsidae:Diptera)的雄性具有腹部附属物,这些附属物在许多方面都很出色。他们是性二态的,有复杂的得失进化史,并且可以连接,因此高度移动。sternite刷子广泛用于复杂的求偶行为,这些行为在物种之间和交配过程中差异很大。腹部附件具有从组织母细胞巢而不是想象盘发育的新发育途径。
我们专注于细胞数量的进化,巢区,以及两性的节段长度,以了解该组织如何与新型腹部附件的形成有关。我们将10个属的17个物种的游荡期幼虫的组织母细胞巢大小映射到Sepsidae的系统发育树,并证明了腹部附属物需要在大多数物种中显着增加组织母细胞巢的大小和细胞数量,而一个物种即使没有这样的修饰也会产生小的附属物。在附属物特别大的物种中,不仅仅是第四个的巢,但是相邻部分的巢扩大了(Themirabiloba,Themiraputris)。腹部附件的丢失对应于第四个组织母细胞扩大的丢失,尽管有一个物种显示出这种模式的例外。构成腹部附件独立起源的一种物种(Perochaetadikowi)使用了一种不寻常的发育机制,因为组织母细胞巢的大小不是性二态的。
组织细胞大小和性二态性程度的惊人的高多样性表明,用于隔膜中腹部附件形成的发育机制具有高度适应性。附属物的存在通常与组织母细胞数量的增加有关,在大多数情况下,附属物的丢失会导致恢复到祖先的组织母细胞形态。然而,我们还发现了一些例外,这些例外表明腹部附件具有可延展的发育起源,该起源对选择有反应。
The males of some sepsid species (
Sepsidae: Diptera) have abdominal appendages that are remarkable in several ways. They are sexually dimorphic, have a complex evolutionary history of gain and loss, and can be jointed and thus highly mobile. The sternite brushes are used extensively in complex courtship behaviors that differ considerably between species and during mating. The abdominal appendages have a novel developmental pathway developing from histoblast nests rather than imaginal discs.
We focus on the evolution of cell number, nest area, and segment length in both sexes to understand how this tissue relates to the formation of novel abdominal appendages. We map histoblast nest size of wandering-phase larvae of 17 species across 10 genera to a phylogenetic tree of
Sepsidae and demonstrate that abdominal appendages require significant increases of histoblast nest size and cell number in most species while one species produces small appendages even without such modifications. In species with particularly large appendages, not only the nests on the fourth, but nests in neighboring segments are enlarged (Themira biloba, Themira putris). The loss of abdominal appendages corresponds to the loss of an enlarged fourth histoblast nest, although one species showed an exception to this pattern. One species that constitutes an independent origin of abdominal appendages (Perochaeta dikowi) uses an unusual developmental mechanism in that the histoblast nest sizes are not sexually dimorphic.
The surprisingly high diversity in histoblast size and degree of sexual dimorphism suggests that the developmental mechanism used for abdominal appendage formation in sepsids is highly adaptable. The presence of appendages usually correlate with increased histoblast cell number and in most cases appendage loss results in a return to ancestral histoblast morphology. However, we also identify several exceptions that indicate the abdominal appendages have a malleable developmental origin that is responsive to selection.