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.
Highlights
Alternative reproductive tactics in animals are commonly associated with distinct male phenotypes resulting in polymorphism of sexually selected weapons such as horns and spines
Sexual selection has driven the evolution of a spectacular array of male weaponry and alternative reproductive tactics (ARTs) among animals[1,2]
Genetic trimorphisms with distinct male phenotypes have been identified in species such as side-blotched lizards[13] and damselflies[14], where morphs are determined by the inheritance of allele combinations at one or few loci and are not condition-dependent; for any given body size males can exhibit one of a number of forms
Summary
Alternative reproductive tactics in animals are commonly associated with distinct male phenotypes resulting in polymorphism of sexually selected weapons such as horns and spines. Genetic trimorphisms with distinct male phenotypes have been identified in species such as side-blotched lizards[13] and damselflies[14], where morphs are determined by the inheritance of allele combinations at one or few loci and are not condition-dependent; for any given body size males can exhibit one of a number of forms. Male Gouldian finches (Erythrura gouldiae) exhibit one of three head colours, which influences complex dominance-related interactions among the three morphs[15], and polymorphism appears to be maintained through frequency-dependent selection These male traits can be used to signal dominance to other males[13,14,15,16], to our knowledge, no examples of genetic polymorphisms in weaponry (outgrowths used in physical combat) have been described. Despite male morphs typically being described by discrete models of either genetic polymorphism or phenotypic plasticity[3], in reality it is unlikely that the mechanisms are so clear cut, and instead there is likely to be an interplay between genes and the environment[19]
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