Multiple exaggerated weapon morphs: a novel form of male polymorphism in harvestmen

Abstract

Alternative reproductive tactics in animals are commonly associated with distinct male phenotypes resulting in polymorphism of sexually selected weapons such as horns and spines. Typically, morphs are divided between small (unarmed) and large (armed) males according to one or more developmental thresholds in association with body size. Here, we describe remarkable weapon trimorphism within a single species, where two exaggerated weapon morphs and a third morph with reduced weaponry are present. Male Pantopsalis cheliferoides harvestmen display exaggerated chelicerae (jaws) which are highly variable in length among individuals. Across the same body size spectrum, however, some males belong to a distinct second exaggerated morph which possesses short, broad chelicerae. Multiple weapon morphs in a single species is a previously unknown phenomenon and our findings have significant implications for understanding weapon diversity and maintenance of polymorphism. Specifically, this species will be a valuable model for testing how weapons diverge by being able to test directly for the circumstances under which a certain weapon type is favoured and how weapon shape relates to performance.

All the better to bite you with! Striking intrasexual differences in cheliceral size define two male morphs in an Amazonian arachnid

“…A single reported case of intrasexual male polymorphism in harvestmen related to cheliceral size has previously been reported. In Pantopsalis cheliferoides (suborder Eupnoi), Painting et al (2015) described males with long-slender chelicerae, with short-broad chelicerae and with short-slender chelicerae. Males of these three morphs have a much longer basal segment of the chelicerae in For all traits we present the slope b, the 95% confidence interval of the slope, and the sample size in parentheses.…”

“…Based on analysis of a large sample of males, we found great and possibly discontinuous variation in cheliceral size, suggesting the existence of intrasexual dimorphism in this species. Recently, male polymorphism in cheliceral size and shape has been reported for the New Zealand harvestman Pantopsalis cheliferoides (Eupnoi: Neopilionidae), which uses the enlarged chelicerae in contests for access to females (Painting et al, 2015). Among species of the suborder Laniatores, however, there is no report of intrasexual male dimorphism based on formal statistical and allometric analyses (reviewed by Buzatto & Machado, 2014).…”

Intrasexually selected weapons

“…Therefore, it is not surprising to find polymorphisms in ISW expression. Polymorphisms in ISWs are frequently related to alternative reproductive strategies that generate alternative reproductive phenotypes (reviews in Gross, ; Herberstein et al, ; see an exception in Painting et al, ). In some species, two or more sympatric male morphs show variations in the development of ISWs, with one form showing more enlarged weapons than the other (e.g.…”

Multiple male morphs in the leaf‐footed bug Mictis longicornis (Hemiptera: Coreidae)

“…When it comes to direct competition, a small or absent sexually selected trait should provide little to no benefit (Buzatto et al 2014). Therefore, for the presence of discrete morphs to be maintained, minor males are expected to find alternative ways to secure reproductive success (Goldsmith 1987;Gross 1996;Emlen 1997;Oliveira et al 2008;Buzatto et al 2014). Consequently, male dimorphism is frequently associated with alternative reproductive tactics.…”

“…To investigate the distribution of abdominal thickness for males and females, we used the package mixsmsn (Prates & Cabral 2009) implemented in R v3.3.1 (R Core Team 2016) to fit finite mixture models that had 1, 2, or 3 skew-normal distributions to the data (Painting et al 2015). We decided to include bi-and tri-modal distributions (i.e.…”