Dispersal and ejaculatory strategies associated with exaggeration of weapon in an armed beetle

Abstract

Weapons used in male fighting can be costly to males and are often reported to trade off with other characters such as wings or spermatogenic investment. This study investigated whether increased investment into weapons can generate evolutionary changes in mating strategy for armed males. Male flour beetles, Gnatocerus cornutus, have enlarged mandibles that are used in male -male competition. We subjected these weapons to 12 generations of bidirectional selection and found trade-offs between weapons and two other male characters: wing and testis size. In addition, probably as a consequence of the observed changes in investment, dispersal ability and ejaculatory volume differ significantly between the lines. This indicates that the exaggeration of a weapon can be associated with dispersal and ejaculatory strategies. Thus, altered investment into weapons can lead to correlated changes in life-history traits.

Sexual conflict over mating in Gnatocerus cornutus ? Females prefer lovers not fighters

“…This is despite the fact these fighter males enjoy significant mating advantages when in direct competition for females [39,43,44]. Instead, females prefer to mate with males that court more, but as noted, in competitive mating situations, females mate with the more competitive phenotypes.…”

“…Males fight using their enlarged mandibles, a character females lack [41,42], with weapon size determining fight outcomes-males with larger mandibles are better fighters. Mandible size is also positively genetically associated with competitive mating success [39,43,44], but daughters sired by large-weaponed males have lower fitness owing to intralocus sexual conflict [39]. However, there is little known about male attractiveness and the fitness consequences of female mate choice in these beetles, and these issues are the focus of this study.…”

“…These individuals were allowed to remain in their developmental vials with fresh food (4 g) for 14 days post-eclosion, allowing sufficient time for males to reach full sexual maturity (see above). Subsequently, the testes were removed from the body using a fine forceps and carefully separated from the surrounding tissue in deionized water following Yamane et al [44]. The length (L) and width (W ) of both testes were measured to the nearest 0.01 mm with the dissecting microscope monitoring system (VM-60, Olympus, Tokyo, Japan), and testis volume (mm 3 ) was calculated using the formula V ¼ (pLW 2 )/6.…”

Is diversification in male reproductive traits driven by evolutionary trade-offs between weapons and nuptial gifts?

“…Another example is from the flour beetle Gnatocerus cornutus which has sexually dimorphic enlarged mandibles. Artificial selection for increased relative mandible size in males reduced relative wing size, whereas artificial selection for decreased relative mandible size resulted in increased relative wing size [6,7]. Importantly, these morphological trade-offs also resulted in functional costs as those males with the largest mandibles, but smallest wings had the lowest dispersal frequencies [7].…”

Histone deacetylases control module-specific phenotypic plasticity in beetle weapons

“…The trade-off relationship between the weapon and flight apparatus is often observed as a characteristic of weaponed insects, reflecting the diverse reproductive strategy of males (48)(49)(50). A distinct type of HDAC (e.g., HDAC1, HDAC3) that causes antagonistic responses to the mandible and wing may be associated with the trade-off relationship, but further investigations of the epigenetic status of the genes involved in mandible and wing development are required to confirm this possibility.…”