Sexual selection mediated by the thermoregulatory effects of male colour pattern in the ambush bugPhymata americana

Abstract

Sexual dimorphism in coloration is a taxonomically widespread phenomenon often attributed to sexual selection on visual signals. However, the ambush bug Phymata americana exhibits sexual dimorphism in coloration that has no apparent signalling function. Here we provide evidence that colour pattern in this species influences male mating success indirectly through its effect on thermoregulation. We demonstrate, using experimental manipulation, that individuals with dark colour pattern achieve higher thoracic temperatures under illumination. We also show that dark colour pattern predicted mate-searching success but only under thermally challenging conditions (i.e. cool ambient temperature). As far as we are aware, this is the first study to provide evidence that sexual dimorphism can be accounted for by sexual selection on thermoregulatory performance.

To quiver or to shiver: increased melanization benefits thermoregulation, but reduces warning signal efficacy in the wood tiger moth

“…The net effect of the cooler climate should make melanization an important fitnessrelated trait because it should benefit mate-finding opportunities in the Alps more compared with central Finland. Similarly, Punzalan et al [23] found that the thermoregulatory benefits of melanin increased fitness in the ambush bug (Phymata americana), but only when temperatures were at the lower limit of tolerance for the species. Although we did not directly link warm-up ability to fitness in our study, previous work on lepidopterans has shown fitness benefits of increased melanization [30][31][32]53].…”

“…The use of dead moths allowed us to control for any differences in thermoregulationrelated behaviour, such as movement, repositioning of wings or differences in metabolic activity that might exist among differently melanized individuals. Previous studies have also used either dry [32] or fresh [23] dead individuals for similar reasons when exploring links between thermoregulation and coloration.…”

“…More melanic individuals may be developmentally hindered because the melanin pigment requires nitrogen [18,19], which is typically a limited resource for herbivorous lepidopterans [20]. However, melanin can also contribute to a more robust immune system [21] and can increase the ability to absorb solar radiation [2,22], which can benefit fitness [23]. At least two documented instances in lepidopterans show increases in melanin coverage with elevation [24,25] and latitude [25,26], suggesting a general link with thermoregulation (see [22] for more examples).…”

Influences of geographic differentiation in the forewing warning signal of the wood tiger moth in Alaska

“…By using dead moths we were able to control for any differences in thermoregulation-related behavior, which might exist among differently melanized individuals. At least two previous studies have also used either dry (Guppy 1986a) or freshly killed (Punzalan et al 2008) individuals for the same reason to look how coloration relates to thermoregulation.…”

“…Thermoregulation in many ectothermic species is important to fitness and benefitted by melanin (Pereboom & Biesmeijer 2003, Trullas et al 2007, Punzalan et al 2008. Melanin is a dark compound found in the coloration of many animals and is thought and shown to trade-off with other fitness-related traits (Talloen et al 2004, Lindstedt et al 2009).…”