Biology Letters最新文献

One assumed function of herbivore-induced plant volatiles (HIPVs) is to attract natural enemies of the inducing herbivores. Field evidence for this is scarce. In addition, the assumption that elicitors in oral secretions that trigger the volatile emissions are essential for the attraction of natural enemies has not yet been demonstrated under field conditions. After observing predatory social wasps removing caterpillars from maize plants, we hypothesized that these wasps use HIPVs to locate their prey. To test this, we conducted an experiment that simultaneously explored the importance of caterpillar oral secretions in the interaction. Spodoptera caterpillars pinned onto mechanically damaged plants treated with oral secretion were more likely to be attacked by wasps compared with caterpillars on plants that were only mechanically wounded. Both of the latter treatments were considerably more attractive than plants only treated with oral secretion or left untreated. Subsequent analyses of headspace volatiles confirmed differences in emitted volatiles that likely account for the differential predation across treatments. These findings highlight the importance of HIPVs in prey localization by social wasps, hitherto underappreciated potential biocontrol agents and provide evidence for the role that elicitors play in inducing attractive odour blends.

Freshwater populations of typically marine species present unique opportunities to investigate biodiversity, evolutionary divergence, and the adaptive potential and niche width of species. A few pinniped species have populations that reside solely in freshwater. The harbour seals inhabiting Iliamna Lake, Alaska constitute one such population. Their remoteness, however, has long hindered scientific inquiry. We used DNA from seal scat and tissue samples provided by Indigenous hunters to screen for mitochondrial DNA and microsatellite variation within Iliamna Lake and eight regions across the Pacific Ocean. The Iliamna seals (i) were substantially and significantly discrete from all other populations ( [Formula: see text]F _st-mtDNA = 0.544, [Formula: see text]Φ _{st - mtDNA} = 0.541, [Formula: see text]F _{st-microsatellites} = 0.308), (ii) formed a discrete genetic cluster separate from all marine populations (modal ∆k = 2, PC1 = 14.8%), had (iii) less genetic diversity (Hd, π, H _exp), and (iv) higher inbreeding (F) than marine populations. These findings are both striking and unexpected revealing that Iliamna seals have likely been on a separate evolutionary trajectory for some time and may represent a unique evolutionary legacy for the species. Attention must now be given to the selective processes driving evolutionary divergence from harbour seals in marine habitats and to ensuring the future of the Iliamna seal.

Haplodiploids-in particular, wasps-are the workhorses of sex-allocation research. This is owing to their unusual system of sex determination, which provides a ready means of sex ratio adjustment. Notably, their sexually asymmetrical mode of genetic inheritance leads mothers and fathers to come into conflict over the sex ratio of their offspring. In the simplest outbreeding scenario, a mother is favoured to employ an even sex ratio while a father prefers that all his mate's offspring are female. An important modulator of evolutionary conflict between mating partners is genetic relatedness, raising the possibility that this sex ratio conflict is reduced in low-dispersal settings with mating occurring between relatives. However, the impact of population viscosity on sex ratio conflict in haplodiploids remains unknown. Here, we develop and analyse a kin-selection model to investigate how the rate of dispersal modulates sex ratio conflict in a haplodiploid, viscous population setting. We find that population viscosity is associated with a reduction in the extent of sex ratio conflict-the effect being very weak under density-independent dispersal and much stronger under density-dependent dispersal.

When risk is unpredictable, organisms may evolve induced defenses, which are activated after an indication of increased risk. In colonies with behavioural specialization, investment in defence may not be uniformly beneficial among group members. Instead, it should depend on the individual's likelihood of participating in defence. The ant Temnothorax longispinosus uses venom to defend against raids by the social parasite Temnothorax americanus. We tested whether T. longispinosus upregulate investment in venom after experiencing a raid, investigating the relationship between venom volume and worker behavioural caste. Overall, raided colonies had more venom per capita than unraided colonies. When divided into behavioural castes, foragers had more venom after experiencing a raid, while nurses did not. These results demonstrate that T. longispinosus have an induced chemical defence against parasitic raids. However, instead of this defence being deployed uniformly among all workers, the induction of the defence depends on the behavioural caste, and therefore age, of the worker, implying that plasticity in venom production increases with age. Since older social insect workers tend to perform riskier tasks, inducibility may align with an increase in expected risk of death, especially if foragers are more likely to defend the colony against parasites than younger workers.

Dinosaurs potentially originated in the mid-palaeolatitudes of Gondwana 245-235 million years ago (Ma) and may have been restricted to cooler, humid areas by low-latitude arid zones until climatic amelioration made northern dispersals feasible ca 215 Ma. However, this scenario is challenged by new Carnian Laurasian fossils and evidence that even the earliest dinosaurs had adaptations for arid conditions. After becoming globally distributed in the Early-Middle Jurassic (200-160 Ma), dinosaurs experienced vicariance driven by Pangaean fragmentation. Regional extinctions and trans-oceanic dispersals also played a role, and the formation of ephemeral land connections meant that older vicariance patterns were repeatedly overprinted by younger ones, creating a reticulate biogeographic history. Palaeoclimates shaped dispersal barriers and corridors, including filters that had differential effects on different types of dinosaurs. Dinosaurian biogeographic research faces many challenges, not the least of which is the patchiness of the fossil record. However, new fossils, extensive databasing and improved analytical methods help distinguish signal from noise and generate fresh perspectives. In the future, developing techniques for quantifying and ameliorating sampling biases and modelling the dispersal capacities of dinosaurs are likely to be two of the key components in our modern research programme.

Host genetic variability can modulate infection resistance, although its role in infection clearance remains unclear. Hookworm disease (Uncinaria sp.) is the leading cause of pup mortality in several otariid species, although the parasite can be cleared through immune-mediated processes. We evaluated the association of host genetic diversity, body condition and immune response with hookworm resistance and/or clearance in the South American fur seal (Arctocephalus australis). Uninfected pups had higher heterozygosity than parasitized individuals, indicating a negative relationship between heterozygosity and the chances of infection. Likewise, pups that died of hookworm infection had lower heterozygosity than those that died of non-infectious causes. Interestingly, once infected, pups that survived hookworm infection had heterozygosities similar to pups that died of hookworm disease. However, pups that cleared the infection had a higher body mass and parasite-specific immunoglobulin G levels than those that did not recover or died of hookworm disease. Thus, although heterozygosity predicted resistance to and mortality from hookworm infections, it did not affect parasite clearance, which was facilitated by better body condition and adaptive immune responses. This demonstrates that host genetic variability and host-environment interactions influence disease dynamics, acting at different, well-defined stages of infection.

Many animals adapt their activity patterns to the best environmental conditions using daily rhythms. African mole-rats are among the mammals that have become models for studying how these rhythms can be entrained by light or temperature in experimental laboratory studies. However, it is unclear whether they exhibit similar circadian rhythms in their natural lightless, subterranean environment. In this study, we used biologging to investigate the activity rhythms of wild, highveld mole-rats. We show that their activity cycle exhibited an ultradian rhythm with a length between 4 and 8 h. On an individual level, mole-rats displayed about five activity bouts per day, occurring at various times during the day and night. On a population level, activity peaked in the afternoon, coinciding with the peak in ambient temperature. Our research suggests that wild subterranean mammals, which experience reduced environmental variation, are unlikely to show clear circadian rhythmicity in activity patterns. Instead, activity periods are distributed over several bouts throughout the day and night, and activity coincides with the peak in daily temperature. We propose that ultradian rhythms in activity may be more common than previously thought and discuss how physiological processes may generate differences in periodicity between laboratory and wild populations.

Mating between closely related individuals can result in a reduction in offspring fitness, known as inbreeding depression. Here, we investigate whether breeding with close relatives affects the reproductive output of parents and the development of their offspring in Damaraland mole-rats (Fukomys damarensis), a cooperatively breeding species where females avoid mating with familiar individuals. By cross-fostering litters of pups soon after birth, we were able to form breeding pairs from full siblings that were reared apart. We compared the reproductive output of these sibling pairs and the survival and growth of their pups with that of unrelated pairs over a period of 4 years. The litter sizes and interbirth intervals of sibling pairs did not differ from those of unrelated pairs, but the growth and survival of inbred offspring were lower, showing that breeding between close relatives is associated with substantial fitness costs. This study suggests that inbreeding depression is an important driver of the extreme reproductive skew observed in social mole-rats. Studies of the costs of inbred matings are now needed in similar species, such as naked mole-rats (Heterocephalus glaber), where captive females more commonly breed with close relatives, to determine whether these costs are lower than in Damaraland mole-rats.

Mosquitoes are the deadliest vectors of diseases. They impose a huge health burden on human populations spreading parasites as disparate as protozoans (malaria), viruses (yellow fever and more) and nematodes (filariasis) that cause life-threatening conditions. In recent years, mating has been proposed as a putative target for population control. Mosquitoes mate mid-air, in swarms initiated by males and triggered by a combination of internal and external stimuli. As the number of females in a swarm is limited, there is intense competition among males, and they 'retune' their physiology for this demanding behaviour. There is limited knowledge on the 'genetic reprogramming' required to enable swarming. Interestingly, recent evidence indicates that the upregulation of circadian clock genes may be involved in the swarming of malaria mosquitoes of the genus Anopheles. Here, we use whole-head RNA-seq to identify gene expression changes in Aedes aegypti males that are engaged in swarming in a laboratory setting. Our results suggest that in preparation to swarming, males tend to lower some housekeeping functions while increasing remodelling of the cytoskeleton and neuronal connectivity; the transcription of circadian clock genes is unaffected.

Integrating information across sensory modalities enables animals to orchestrate a wide range of complex behaviours. The relative importance placed on one sensory modality over another reflects the reliability of cues in a particular environment and corresponding differences in neural investment. As populations diverge across environmental gradients, the reliability of sensory cues may shift, favouring divergence in neural investment and the weight given to different sensory modalities. During their divergence across closed-forest and forest-edge habitats, closely related butterflies Heliconius cydno and Heliconius melpomene evolved distinct brain morphologies, with the former investing more in vision. Quantitative genetic analyses suggest that selection drove these changes, but their behavioural consequences remain uncertain. We hypothesized that divergent neural investment may alter sensory weighting. We trained individuals in an associative learning experiment using multimodal colour and odour cues. When positively rewarded stimuli were presented in conflict, i.e. pairing positively trained colour with negatively trained odour and vice versa, H. cydno favoured visual cues more strongly than H. melpomene. Hence, differences in sensory weighting may evolve early during divergence and are predicted by patterns of neural investment. These findings, alongside other examples, imply that differences in sensory weighting stem from divergent investment as adaptations to local sensory environments.