Differences in the reproductive behaviour and larval development of two Canthon rutilans subspecies reinforce their thermal regional segregation

Two dung beetle subspecies of Canthon rutilans Castelnau (Coleoptera: Scarabaeidae, Scarabaeinae), C. rutilans rutilans and C. rutilans cyanescens, inhabit different environmental temperature conditions in southern Brazil. We developed a laboratory breeding experiment with 60 pairs of individuals of the two subspecies at five temperature conditions (from 15 to 35 °C) to compare the influence of temperature on the behaviour of adults and the development of larvae. The behavioural patterns of the adults in both subspecies differ according to temperature. The size of food balls was smaller and lighter in C. rutilans cyanescens. Although temperature did not influence the feeding behaviour (measured as the number of food balls made), reproductive behaviour (measured as the number of brood balls made by pair) was significantly lower at 15 °C for both subspecies. Besides that, brood balls from C. rutilans rutilans were bigger and heavier at lower temperatures. The number of offspring and the time of emergence depend on temperature too. However, the weight of the offspring and the longevity of adults depend on the subspecies and temperature treatment. These results demonstrate that the subspecies have different thermal adaptations: C. rutilans rutilans has reproductive behaviour adapted to living under colder and broader conditions than C. rutilans cyanescens.     

Generalist dung attraction response in a New Zealand dung beetle that evolved with an absence of mammalian herbivores

1. Dung beetles (Scarabaeidae: Scarabaeinae) are integral parts of many ecosystems because of their role in decomposition of dung; particularly mammal dung, which forms the diet of both larvae and adults. 2. New Zealand dung beetles are unusual as they are flightless and evolved on islands with a highly depauperate mammal fauna and thus without the usual dung resource used by dung beetles elsewhere. The diet of New Zealand dung beetles is unknown. 3. We hypothesised (1) that the endemic dung beetle Saphobius edwardsi would be attracted to a broad range of food types, and (2) that S. edwardsi would be able to survive and reproduce on a range of dung types and puriri (Vitex lucens) humus. 4. Laboratory choice tests identified that S. edwardsi was attracted to a range of mammal, bird, invertebrate, and reptile dung types, but not to non‐dung food sources. Five‐month no‐choice tests found that beetle survival rates were lower for beetles fed with humus compared with those fed on mammal, bird, or invertebrate dung. None of the beetles reproduced. 5. This study suggests S. edwardsi have a strong preference for dung, and are likely to be broad dung generalists in their feeding behaviour.     

Global distribution patterns provide evidence of niche shift by the introduced African dung beetle Digitonthophagus gazella

The establishment of cattle ranches throughout the world has prompted the release of dung beetles as biological control agents that reduce pasture fouling and control dung-breeding flies. One of these beetles, Digitonthophagus gazella (Fabricius) (Coleoptera: Scarabaeidae), that is native to southeast Africa, has been introduced into the Americas, Australia, and New Zealand. Distribution records for this species have been used to develop climate models of potential future establishment. Recent studies, however, identify D. gazella as a complex of seven species. Taking into account this revision, and the clear identification of the records belonging to the actual D. gazella, we developed environmental models to identify factors that have contributed to the establishment of this species across regions and habitats. We compared the environmental conditions of D. gazella in its native range against those in the regions where the species has or has not established. Our results indicate that D. gazella is still absent in certain parts of Central and South America and parts of Africa where it could potentially establish. We speculate that its distribution in Africa is limited by competitive exclusion. The introduction of D. gazella in America is relatively recent, such that the full extent of its distribution has probably yet to be realized. In Australia and North America, D. gazella is present in regions not predicted according to its native environmental conditions. This discrepancy may reflect a lack of competitive exclusion, phenotypic plasticity, and/or genetic adaptation. Our analyses suggest that the species has the ability to adapt to a wide range of environmental conditions that are extremely different from those in their native region. The species represents a useful case study to indicate that an introduced species may expand its realized niche beyond what is expected based on apparent environmental limits in the species native range.