Biology Letters最新文献

How symbionts acquired hosts and diversified phylogenetically during their evolutionary history is a focus of attention in many symbiotic taxa. Marine polyclad flatworms are usually free-living, but some are symbiotic, using animals as hosts. However, the history of their acquisition of symbiotic systems is not well understood. Therefore, we focused on mollusc symbiotic flatworms in the suborder Acotylea and investigated the host specificity and phylogenetic history of the acquisition of symbiosis. Field surveys revealed that symbiotic flatworms utilized certain molluscs as hosts. In particular, Stylochoplana pusilla and Stylochoplana parasitica utilized different molluscan species as hosts sympatrically. The phylogenetic analysis and the ancestral state reconstruction indicate that the mollusc symbiotic flatworms formed a monophyletic group and that their common ancestor shifted from free-living to mollusc symbiosis. These results suggest that each of the flatworms did not independently acquire a symbiotic system with molluscan hosts during its phylogenetic history, but that their common ancestor acquired a mollusc symbiotic system, which then underwent acquisition of host specificity and speciation. This study emphasizes that multiple host use can be a driving force for niche advancement and speciation in the symbionts.

Inter-specifically, mammalian species with larger brains built of numerous neurons have higher cognitive abilities (CA) but at the expense of higher metabolic costs. It is unclear, however, how this pattern emerged since evolutionary mechanisms act intra-specifically, not inter-specifically. Here, we tested the existence of the above pattern at the species level in the hippocampus-the brain structure underlying CA. We used an artificial selection experiment consisting of lines of laboratory mice divergently selected for basal metabolic rate (BMR)-a trait implicated in brain size evolution, its metabolic costs and CA. Selection on BMR did not affect hippocampus size as a correlated response to this selection. However, the high BMR mice had superior CA and manifested increased neuronal density, higher cytochrome c oxidase density (indexing metabolic costs of neuronal activity) and dendritic spine density (indexing connectivity between neurons). Thus, our study calls into question the generality of patterns of the evolution of CA apparent interspecifically. At the species level, increased CA may arise through the rearrangement of the architecture and function of neurons without a conspicuous increase in their size but increase metabolism.

Female exposure to seminal fluid influences multiple aspects of reproductive physiology. We tested the hypothesis that extended exposure to seminal fluid prior to pregnancy provides fertility benefits, as predicted from human studies linking seminal fluid exposure to a reduced incidence of pregnancy disorders. Female mice were co-housed for five months with either vasectomized males (producing seminal plasma but not sperm), vasectomized males without seminal vesicles (producing neither seminal plasma nor sperm), intact males or other females, before mating all females with intact males to assess pregnancy outcomes. We found an increase in litter size at birth in females previously exposed to vasectomized males that was not evident after mating with seminal vesicle-excised males, although the latter comparison had less power. However, postnatal loss of offspring led to similar litter sizes between groups at weaning. In a second study, we observed that females previously housed with vasectomized males and later mated to intact males maintained more fetuses compared with naive females in late pregnancy. Placental morphology was also altered with a significant decrease in the size of the labyrinthine zone, a sign of increased placental efficiency. These results provide experimental evidence that preconception seminal fluid exposure in the absence of conception can improve later pregnancy outcomes in mice.

Selection can act in a sex-specific manner on cognitive abilities, including numerosity, especially when ecological roles differ between sexes. However, few systems exist in which numerical abilities would be expected to differ between the sexes, and even fewer focus on systems in which females are predicted to outperform males. In obligate brood-parasitic brown-headed cowbirds (Molothrus ater), only females select and parasitize host nests, and would benefit from enhanced numerical abilities to distinguish suitable host nests in the process of egg laying from unsuitable nests that have begun incubation. To test this hypothesis, we trained cowbirds to use touchscreens and discriminate between sets of images differing in number. Cowbirds distinguished images based on number alone (i.e. without using non-numerical cues), and females outperformed males across combinations of objects ranging from one to six (range in host egg numbers), but this difference disappeared across higher numbered combinations. In addition, males spent less time deciding on the correct stimulus than females, but made less accurate decisions overall, suggesting they 'guessed' correct answers more than females. We add to the growing evidence for complex numerical abilities in diverse taxa, and show these abilities can be shaped by ecology in a sex-specific way.

Animals often eavesdrop on other species' alarm calls to gain information about danger, but this can allow for deception by callers. Such deception often uses 'aerial' alarm calls, which normally warn of airborne predators and prompt immediate fleeing. The calls are deceptive if they are given when no flying predator is present and the caller benefits from the victim's response, typically by gaining food dropped when the listener flees. We studied deceptive alarm calling by brown thornbills, Acanthiza pusilla, defending offspring against predatory pied currawongs, Strepera graculina. Thornbills give their own and mimetic aerial alarm calls when defending nestlings against currawongs, who are fooled into scanning for danger or flying away. We tested whether deception works by exploiting the predator's response to aerial alarm calls, and what role mimicry plays. Currawongs were more likely to flee, and delayed feeding longer, after playback of purely aerial compared with purely mobbing alarm choruses. They responded the same regardless of what type of mimetic alarm followed the thornbill's aerial alarm. We conclude that vocal deception is effective because it exploits currawong response according to call meaning, while mimicry likely creates an illusion of a multi-species alarm chorus.

The northern star coral, Astrangia poculata, is a temperate, facultatively symbiotic, scleractinian coral spanning the coastal western Atlantic. This calcifying species is mixotrophic with a broad geographical range, and therefore has high utility in addressing questions related to community ecology, symbiosis, population genetics, biomineralization and resilience to environmental perturbations. Here, we review the current A. poculata peer-reviewed literature, which is primarily found in six focal areas: geographic range, habitat and ecology, symbiosis, life history, microbiome and genomics and transcriptomics. A cross-cutting theme of these studies emerges as the value of an experimental system that is facultatively symbiotic. Yet, the historic overgeneralization of symbiotic versus 'aposymbiotic' A. poculata has constrained the interpretation of the basic biology and generalizability of conclusions. Emergent from our review, and timely with respect to climate change, is the value that A. poculata brings as an experimental system with the potential to test questions on range adaptability and environmental resilience. We identify future avenues of research for A. poculata studies that include integration of population genetics with organismal-molecular-cellular biology across the geographical range, while leveraging the power of the facultative symbiosis context.

Two enduring ideological divisions in biodiversity conservation concern whether conservation should prioritize (i) the interests of people or wild animals and (ii) the interests of individual animals or groups of animals. Public debates suggest that people living in the Global North more strongly prioritize the interests of wild animals over people and the interests of individual animals over groups of animals. To examine this possibility, we measured and compared conservation priorities across 10 international publics living in rural and urban areas of sub-Saharan Africa, the United States of America (USA) and the United Kingdom (UK). Overall, distant respondents (i.e. living in the UK, USA and urban sub-Saharan Africa) more strongly prioritized the interests of wild animals over people and the interests of individual animals over groups of animals. Moreover, variation among local publics (i.e. living in high-biodiversity areas of rural sub-Saharan Africa) was greater than among distant publics. Our findings illuminate how ideological divisions may complicate international biodiversity conservation, especially around controversial topics such as culling, hunting, transloaction and protected-areas management. Policies and programmes more acceptable to distant people may be less acceptable to local people, creating difficulties for decision-makers charged with balancing biodiversity conservation alongside the values, needs, interests and concerns of multiple publics.

Aggression and its neurochemical modulators are typically studied in males, leaving the mechanisms of female competitive aggression or dominance largely unexplored. To better understand how competitive aggression is regulated in the primate brain, we used receptor autoradiography to compare the neural distributions of oxytocin and vasopressin receptors in male and female members of female-dominant versus egalitarian/codominant species within the Eulemur genus, wherein dominance structure is a reliable proxy of aggression in both sexes. We found that oxytocin receptor binding in the central amygdala (CeA) was predicted by dominance structure, with the members of three codominant species showing more oxytocin receptor binding in this region than their peers in four female-dominant species. Thus, both sexes in female-dominant Eulemur show a pattern consistent with the regulation of aggression in male rodents. We suggest that derived pacifism in Eulemur stems from selective suppression of ancestral female aggression over evolutionary time via a mechanism of increased oxytocin receptor binding in the CeA, rather than from augmented male aggression. This interpretation implies fitness costs to female aggression and/or benefits to its inhibition. These data establish Eulemur as a robust model for examining neural correlates of male and female competitive aggression, potentially providing novel insights into female dominance.

Gregarious behaviours in modern and fossil arthropods are commonly associated with defensive strategies, mass moulting and synchronous reproduction. Such behaviour is scarcely documented in the crustacean fossil record. Identifying clusters in extinct Pancrustacea is, therefore, important for understanding the evolutionary history and origin of crustacean gregariousness. Cyclida, an order of extinct, enigmatic pancrustaceans that have been subject to limited palaeoecological examination, represents an ideal group for testing the presence of gregarious behaviour. Here, we report a cluster of 50 Schramine montanaensis individuals from the Serpukhovian-aged Bear Gulch Limestone of Montana, USA, expanding the exceptionally rare record of cyclidan aggregations. The presence of articulated specimens with appendages and possible gill preservation supports the interpretation of carcasses that were preserved during a rapid burial event. We propose that this cluster records either a mass moulting event or clustering for shelter, representing one of the oldest records of crustacean gregariousness. These findings provide important insights into cyclidan life modes and ecological interactions in Carboniferous marine environments.