Responses of Tribolium castaneum to olfactory cues from cotton seeds,the fungi associated with cotton seeds,and cereals

We tested, in an olfactometer, whether or not Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) responds preferentially to the volatiles that emanate from the fungi associated with cotton [Gossypium hirsutum L. (Malvaceae)] seed over those that emanate from cereals, because cereals are usually portrayed as the primary resources of these beetles. Pairwise comparisons were conducted between cotton seed, wheat (Triticum aestivum L.), and sorghum [Sorghum bicolor (L.) Moench] (both Poaceae); volatiles were tested from intact seeds and from both water and ethanol extracts. The results demonstrate that T. castaneum is attracted more strongly to cotton seeds with its lint contaminated with fungi, than to the conventional resources of this species (i.e., wheat and sorghum). Further tests prove that it is the fungus on the lint that produces the active volatiles, because the beetles did not respond to sterilized cotton lint (i.e., without the fungi typically associated with it when cotton seed is stored). Tests with five fungal cultures (each representing an unidentified species that was isolated from the field‐collected cotton lint) were variable across the cultures, with only one of them being significantly attractive to the beetles. The others were not attractive and one may even have repulsed the beetles. The results are consistent with the beetles having a strong ecological association with fungi and suggest it would be worth investigating the ecology of T. castaneum from this perspective.     

The interaction effect between intraspecific competition and seed quality on the life‐history traits of the seed‐feeding beetle Acanthoscelides macrophthalmus

It has been shown that intraspecific competition and resource quality may affect life‐history traits of insects, such as body size, fecundity, and survival. However, intraspecific competition and resource quality may interact with each other. The study of such interacting effects is crucial for understanding the influence of these ecological variables on the selection of specific life‐history traits. Here, we investigated whether the interaction between intraspecific larval competition and variation in resource quality affects adult emergence and survival, egg size, fecundity, body size, and sexual size dimorphism (SSD) of the seed‐feeding beetle Acanthoscelides macrophthalmus (Schaeffer) (Coleoptera: Chrysomelidae: Bruchinae) when infesting Leucaena leucocephala (Lam.) De Wit (Fabaceae), its host plant. In the laboratory, beetles were reared on seeds that differed in quality (e.g., different hardness, seed size, water content), in the presence or absence of larval competition. Body size and SSD did not differ between treatments (with and without competition), nor were they affected by varying resource quality. Females subjected to competition during the larval stage and females emerging from seeds of higher quality, displayed the highest fecundity. The proportion of emergent adults was higher in the absence of competition. In addition, larger eggs were laid on the low‐quality resource in the absence of competition, showing a trade‐off between egg size and egg number. Adult survival differed among treatments and resource qualities, suggesting a higher investment in adult survival for individuals emerging from seeds of low quality in the presence of competition. Whether changes in specific traits could be selected for in detriment of others will depend on the strength of intraspecific competition, the variation in resource quality, and the plasticity in the life‐history traits investigated. This needs further clarification.     

Genetic evidence for male‐biased dispersal in the Qinghai toad‐headed agamid Phrynocephalus vlangalii and its potential link to individual social interactions

Sex‐biased dispersal has profound impacts on a species' biology and several factors have been attributed to its evolution, including mating system, inbreeding avoidance, and social complexity. Sex‐biased dispersal and its potential link to individual social interactions were examined in the Qinghai toad‐headed agamid (Phrynocephalus vlangalii). We first determined the pattern of sex‐biased dispersal using population genetic methods. A total of 345 specimens from 32 sites in the Qaidam Basin were collected and genotyped for nine microsatellite DNA loci. Both individual‐based assignment tests and allele frequency‐based analyses were conducted. Females revealed much more genetic structure than males and all results were consistent with male‐biased dispersal. First‐generation migrants were also identified by genetic data. We then examined eight social interaction‐related morphological traits and explored their potential link to sex‐biased dispersal. Female residents had larger heads and longer tails than female migrants. The well‐developed signal system among females, coupled with viviparity, might make remaining on natal sites beneficial, and hence promote female philopatry. Dominant females with larger heads were more likely to stay. Contrary to females, male migrants had larger heads and belly patches than residents, suggesting that dispersal might confer selective advantages for males. Such advantages may include opportunities for multiple mating and escaping from crowded sites. Large belly patches and several other morphological traits may assist their success in obtaining mates during dispersal. Furthermore, a relatively high relatedness (R = 0.06) among females suggested that this species might have rudimentary social structure. Case studies in “less” social species may provide important evidence for a better understanding of sex‐biased dispersal.