Annual reproductive phenology of the coprophagous beetleDichotomius satanas(Coleoptera: Scarabaeidae, Scarabaeinae) of the cloud forest in eastern Mexico

Abstract

Reproductive phenology of organisms is modulated by biotic and abiotic factors, with direct effects on the demography. This study describes the annual reproductive phenology of Dichotomius satanas (Harold, 1867) (Coleoptera: Scarabaeidae, Scarabaeinae) of the cloud forest in eastern Mexico, through the morphological changes in the reproductive systems of individuals and their relationship with climatic conditions. Three stages of sexual maturity were recognised as occurring throughout the year: immature, maturing, and mature – with a higher occurrence of immature individuals. Abundance of immature and maturing females was explained by minimum temperature, but none of the environmental variables considered was related to mature females. Abundance of immature and maturing males was related to precipitation, while abundance of mature males was related to minimum temperature and precipitation. The phenology of D. satanas was markedly seasonal with a single peak of abundance corresponding to the reproductive period during the warm and rainy season, thus indicating a univoltine pattern of reproduction. Immature females were recorded before immature males, and no synchrony was observed between the maturing and mature males and females. We provide information pertaining to the reproductive biology of coprophagous beetles and highlight the importance of reproductive phenology as a tool with which to understand future environmental scenarios.

Spatiotemporal variation in the adult sex ratio, male aggregation, and movement of two tropical cloud forest dung beetles

“…In reproductive terms, the bias toward males in D . satanas indicates greater intrasexual competition given that females were proportionally less abundant, they produce a greater number of oocytes (2–9; Barretto et al 2021 ), and both sexes apparently make a smaller parental investment ( Halffter and Matthews 1966 ; Halffter and Edmonds 1982 ). In addition, a lower number of female dung beetles have also been associated with an increase in intra and interspecific competition that limits the availability of the resources needed for feeding and reproduction.…”

“…Several studies have indicated that a higher degree of aggregation and sex ratio biased toward the more common sex are usually found in habitats and during the seasons that offer the better conditions for the survival and reproduction of individuals ( McKellar et al 2009 ; Reichard et al 2014 ). For dung beetles, the reproductive season coincides with an increase in temperature and precipitation during the rainy season ( Halffter and Edmonds 1982 ; Barretto et al 2021 ). The highest aggregation of males was observed for both species during this season, as was the greatest variation in ASR.…”

“…Sex was determined based on sexual dimorphism in D. mexicanum (differences in the tarsal claw shape of the foreleg) and based on secondary sexual characters in D. satanas (presence of horns on head and thorax; Table 1 ). Data were only taken for beetles with a rigid, chitinized exoskeleton as these are considered mature adults or are in the process of maturation ( Halffter and Edmonds 1982 ; Barretto et al 2021 ). The capture–recapture history over time was obtained for each beetle, which in statistical terms is considered the best approach for studies at the population level ( Fujiwara and Caswell 2002 ; Ancona et al 2017 ).…”

“…It is also known that OSR and density vary among populations that are geographically separated ( Moczek 2003 ) and according to House et al (2011) in the dung beetle Ontho phagus taurus , the sex ratio depends on the differential mortality rate between sexes, as a function of the amount of food provided by the parents during nesting. In some dung beetle species (e.g., Dichotomius satanas ) with an annual reproductive cycle, it is common to find sexually immature individuals during much of the year ( Barretto et al 2021 ). This makes ASR a useful estimator, combined with the fact that the sexual maturation of individuals based on external morphological characteristics (e.g., rigid exoskeleton) is difficult to determine ( Barretto et al 2021 ).…”

“…In some dung beetle species (e.g., Dichotomius satanas ) with an annual reproductive cycle, it is common to find sexually immature individuals during much of the year ( Barretto et al 2021 ). This makes ASR a useful estimator, combined with the fact that the sexual maturation of individuals based on external morphological characteristics (e.g., rigid exoskeleton) is difficult to determine ( Barretto et al 2021 ).…”