No abstract

The ability to form cooperative societies may explain why humans and social insects have come to dominate the earth. Here we examine the ecological consequences of cooperation by quantifying the fitness of cooperative (large groups) and non-cooperative (small groups) phenotypes in burying beetles (Nicrophorus nepalensis) along an elevational and temperature gradient. We experimentally created large and small groups along the gradient and manipulated interspecific competition with flies by heating carcasses. We show that cooperative groups performed as thermal generalists with similarly high breeding success at all temperatures and elevations, whereas non-cooperative groups performed as thermal specialists with higher breeding success only at intermediate temperatures and elevations. Studying the ecological consequences of cooperation may not only help us to understand why so many species of social insects have conquered the earth, but also to determine how climate change will affect the success of these and other social species, including our own.DOI: http://dx.doi.org/10.7554/eLife.02440.001

Asynchronous hatching is an important component of animal reproductive strategies, yet it has been studied almost exclusively in altricial birds. In this study, we provide evidence on the adaptive consequences and the heritable basis of asynchronous hatching in an insect, the burying beetle Nicrophorus vespilloides. Parents of this species breed on carcasses of small vertebrates and provide food in the form of predigested carrion for their offspring. We found that the size of the carcass used for breeding had a significant effect on hatching skew towards the earlier part of the hatching period, suggesting that female parents adjust hatching skew facultatively to the amount of resources available for breeding. Using a full sibling breeding design, we also found that parent family had a significant effect on both hatching skew and hatching spread, suggesting that there is a heritable basis to asynchronous hatching. Finally, we found that hatching spread affected offspring survivorship, providing evidence that asynchronous hatching patterns have adaptive consequences in N. vespilloides. Our study provides valuable new insights into the evolution and ecological significance of asynchronous hatching by providing evidence on the adaptive consequences and the heritable basis of asynchronous hatching in a non-avian species.

Our study investigated the fungistatic effects of the anal secretions ofNicrophorus nepalensisHope on mouse carcasses. The diversity of fungi on carcasses was investigated in five different experimental conditions that corresponded to stages of the burial process. The inhibition of fungal growth on carcasses that were treated by mature beetles before burial was lost when identically treated carcasses were washed with distilled water. Compared with control carcasses, carcasses that were prepared, buried, and subsequently guarded by mature breeding pairs of beetles exhibited the greatest inhibition of fungal growth. No significant difference in fungistasis was observed between the 3.5 g and the 18 to 22 g guarded carcasses. We used the growth of the predominant species of fungi on the control carcasses,Trichodermasp., as a biological indicator to examine differences in the fungistatic efficiency of anal secretions between sexually mature and immature adults and between genders. The anal secretions of sexually mature beetles inhibited the growth ofTrichodermasp., whereas the secretions of immature beetles did not. The secretions of sexually mature females displayed significantly greater inhibition of the growth ofTrichodermasp. than those of sexually mature males, possibly reflecting a division of labor in burying beetle reproduction.

Carrion beetles (Nicrophorus spp.) use small vertebrate carcasses for food and reproduction. Their ecology and behaviors are highly affected by the availability of carcasses and the surrounding environmental conditions. Our results revealed that in subtropical Fushan, northern Taiwan, N. nepalensis was mainly active in spring (February to May), and could also be found in autumn (October and November); but there was no capture record in summer (June to September) and winter (December and January). A laboratory temperature tolerance study indicated that N. nepalensis adults become inactive at temperatures above 26°C, and had the highest mortality when the temperature was raised from 27°C to 28°C. Furthermore, N. nepalensis became sexually mature at 20°C, depending on the photoperiod: the longer the day, the lower the percentage of sexually mature 2‐week‐old females after emergence. In another experiment, N. nepalensis virgins were paired under three possible conditions at Fushan. At 15°C and 20°C, if carcasses were presented to the pairs within 3 days after emergence, all laid eggs in the second week after emergence. If carcasses were presented 1 week after emergence, most began to reproduce at 20°C with 12.5 h of daylight. However, at 15°C with 11 h of daylight, the carrion beetles hibernated first, and reproduced in the ninth week after emergence. At 25°C with 14 h of daylight, carrion beetles did not bury the mouse carcasses, the females did not lay eggs, and the adult lifespan was only one‐third of that at 20°C. This study revealed that both photoperiod and temperature influence the time needed to reach the sexual maturity of N. nepalensis; and also implied that the narrow temperature tolerance range and dormancy behavior of carrion beetles are highly regulated by those environmental factors.