Temperature-Dependent Regulation of Reproduction in the Diving Beetle Dytiscus sharpi (Coleoptera: Dytiscidae)

Abstract

The effects of temperature on the mating behavior, gonad development, germ cell maturation, and egg spawning of the predaceous diving beetle Dytiscus sharpi (Coleoptera; Dytiscidae), were investigated. By field observations, we found that mating behavior started in October and occurred more frequently from November to December. Under our laboratory breeding conditions, we observed almost the same seasonal variation in mating behavior. We found that temperatures lower than 20 degrees C were required to trigger mating behavior. We also found the same temperature threshold triggered gonadogenesis as well as spermatogenesis. Furthermore, for females, exposure to lower temperatures (<8 degrees C) during the winter was required for egg maturation and spawning in spring; that is, there was a second threshold for successful female reproduction. We conclude that the termination of summer reproductive diapause of D. sharpi is regulated in a temperature-dependent manner, thus effecting the adaptation of D. sharpi to southern warm habitats.

Gonad development and sperm motility of the diving beetleCybister brevisAubé, 1838 (Coleoptera: Dytiscidae) in response to seasonal changes in Japan

“…Balfour-Browne, 1944, D. carolinus Aub e, 1838, D. cordieri Aub e, 1838, D. dauricus Gebler, 1832, D. fasciventris Say, 1824, D. harrisii Kirby, 1837, D. hybridus Aub e, 1838, and D. verticalis Say, 1823 found in the United States, mate only in the early spring. Similar results were described for D. marginalis Linnaeus, 1758 (Blunck 1912), D. alaskanus (Aiken and Wilkinson 1985), D. sharpi validus R egimbart, 1899 (Yamaguchi 1992), and D. sharpi sharpi Wehncke, 1875 (Inoda 2003;Inoda et al 2007). In the case of D. sharpi sharpi, temperatures lower than 20 C in late autumn (OctoberÀDecember) were required to trigger mating behaviour and gonad development as well as spermatogenesis (Inoda et al 2007).…”

“…For females, egg maturation in winter (JanuaryÀFebruary) and oviposition in early spring (MarchÀApril) require low temperatures (<8 C) (Inoda 2003;Inoda et al 2007). The second threshold observed for females is a physiological feature, i.e., the breakdown of the reproductive diapauses, which ensures successful reproduction (Inoda et al 2007).…”

Female reproductive tract form drives the evolution of complex sperm morphology

“…First, males of some species invest heavily in sperm production (up to 13% of total body mass in Dytiscus sharpi) (32). Second, males of numerous species display behavioral adaptations to reduce sperm competition (i.e., mate guarding and mating plugs) (32)(33)(34)(35).…”

“…First, males of some species invest heavily in sperm production (up to 13% of total body mass in Dytiscus sharpi) (32). Second, males of numerous species display behavioral adaptations to reduce sperm competition (i.e., mate guarding and mating plugs) (32)(33)(34)(35). Third, comparative studies have identified coevolutionary arms races between female mating resistance and male persistence traits (36,37), consistent with a history of polyandry.…”

Choice of Prey Body Parts for Effective Feeding by Predaceous Diving Beetle Larvae, Dytiscus sharpi sharpi (Wehncke) (Coleoptera: Dytiscidae)

“…We used beetle larvae of first (n=138), second (n=123) and third (n=64) instar stages. All observations were carried out at 15°C, the environmental temperature in locations where we captured beetles (Inoda et al 2007). …”