Evolutionary Ecology

Many animals use visual traits as a predator defence. Understanding these visual traits from the perspective of predators is critical in generating new insights about predator–prey interactions. In this paper, we propose a novel framework to support the study of strategies that exploit the visual system of predators. With spiders as our model taxon, we contextualise these strategies using two orthogonal axes. The first axis represents strategies using different degrees of conspicuousness to avoid detection or recognition of the spider and deter predator attacks. The second axis represents the degree of honesty of the visual signal. We explore these issues with reference to the three main vision parameters: spectral sensitivity, visual acuity, and temporal resolution, as well as recent tools to study it, including multispectral digital imaging.

Interspecific mating normally decreases female fitness. In many species, females avoid heterospecific males innately or by imprinting on their parents. Alternatively, adult females could learn to discriminate against heterospecific males after exposure to such males. For example, Syrian hamster (Mesocricetus auratus) females learn to discriminate between conspecific males and Turkish hamster (M. brandti) males during adulthood by exposure to males of both species. Adult females not previously exposed to Turkish hamster males will mate similarly with conspecific and heterospecific males. However, in a previous study we showed that exposure to a heterospecific male and a conspecific male for 8 days led to mating avoidance and aggression towards the heterospecific male. Here we conducted two experiments to investigate how much exposure to the heterospecific male was required for females to avoid mating with the heterospecific male (Experiment 1) and how long that avoidance lasted in the absence of continuous exposure to heterospecific stimuli (Experiment 2). Fast and durable learning would indicate the evolution of an efficient avoidance response. In Experiment 1, females were exposed to a heterospecific male for 1, 4 h, 4 or 8 days and then paired with that male. We found more avoidance of interspecific mating after 4 or 8 days of exposure than after 1 or 4 h of exposure. In Experiment 2, females were exposed to a heterospecific male for 8 days and then paired with that male either 10 min later or 8 days later. We found that after an 8-day delay females were highly sexually receptive to the heterospecific male. Additionally, a comparison between the current experiments and a previous study indicates that female Syrian hamsters do not require concurrent exposure to a conspecific male and a heterospecific male to learn to avoid interspecific mating; exposure to a heterospecific male is sufficient.

Các loài động vật sống phụ thuộc và không phụ thuộc vào hang động đều chơi những vai trò chức năng quan trọng trong hệ sinh thái hang động. Khác với các loài động vật sống phụ thuộc vào hang, các loài động vật sống không phụ thuộc vào hang có thể tồn tại trong cả các môi trường bên trong và bên ngoài hang động. Tuy nhiên, chưa có mô hình nhân khẩu học so sánh nào giải thích sự hiện diện kéo dài của cả các loài động vật sống phụ thuộc và không phụ thuộc vào hang động. Chúng tôi đã phát triển một phân tích đánh giá đa trạng thái bằng phương pháp đánh dấu và tái đánh dấu (CMR) dựa trên 5 năm dữ liệu thu thập từ các hang động ở phía Bắc Alabama, Hoa Kỳ để khám phá sự khác biệt về tỷ lệ sống sót và tỷ lệ chuyển đổi sinh sản giữa các loài tôm hùm sống phụ thuộc (Orconectes australis và Cambarus hamulatus) và không phụ thuộc (C. tenebrosus) trong hang động. Các phân tích CMR đa trạng thái cho thấy rằng các loài tôm hùm sống phụ thuộc đực có tỷ lệ chuyển đổi sang trạng thái sinh sản cao hơn đáng kể so với C. tenebrosus đực, trong khi không có sự khác biệt nào giữa các loài đối với cá thể cái. Tuy nhiên, tỷ lệ chuyển sang trạng thái không sinh sản thì cao hơn cho các loài tôm hùm sống phụ thuộc bất kể giới tính. Tỷ lệ sống sót rõ ràng giữa các loài sống phụ thuộc vào hang và C. tenebrosus không khác nhau, gợi ý rằng kích thước quần thể lớn hơn của các loài động vật sống phụ thuộc trong các khu vực nghiên cứu của chúng tôi có thể được thúc đẩy bởi các chiến lược sinh sản thành công hơn của con đực. Kết quả của chúng tôi gợi ý rằng các loài tôm hùm sống phụ thuộc đã phát triển các chiến lược sinh sản riêng biệt theo giới tính không giống như C. tenebrosus, mà có thể đại diện cho sự thích nghi chuyên biệt với môi trường hang động. Ngược lại, việc di cư liên tục từ các quần thể trên bề mặt là rất quan trọng cho sự hiện diện bền vững của các loài không phụ thuộc trong môi trường hang động.

Populations of the marine gastropod Littorina saxatilis from exposed rocky shores of NW Spain provide one of the few putative cases of sympatric ecological speciation. Two ecotypes with large differences in shell morphology and strong assortative mating are living at different vertical levels of the shore separated by a few meters. It has been hypothesized that shell size is the main determinant for the reproductive isolation observed between the ecotypes, and that several shell shape traits are subject to divergent natural selection and are responsible for the adaptation of each ecotype to its respective habitat. Using embryos extracted from wild females we obtain estimates of genetic variation for shell size and shape and compare them with those from neutral molecular markers. Estimates of heritability are significantly larger for the ecotype found in the upper shore than for that in the lower shore, in concordance with a similar result observed for heterozygosity of neutral markers. The large genetic differentiation between ecotypes for the shell traits, contrasting the smaller close to neutral differentiation between populations of the same ecotype, supports the implication of the traits in adaptation.

In a subdivided population with recurrent local extinction and re-colonisation, competition amongst related pollen or sperm to fertilise ovules or eggs (‘local mate competition’) is expected to select for female-biased sex allocation. Population turnover should also select against unisexuality in favour of self-fertile cosexuality, because males and females are unable to establish new populations on their own (‘Baker's Law’). Here I argue that androdioecy, a rare breeding system in which males co-occur with hermaphrodites, may evolve in a metapopulation under the joint action of local mate competition and Baker's Law if rates of self-fertilisation decrease with increasing population size. The hypothesis makes several predictions regarding patterns of life-history and sex allocation that are borne out by recent observations of androdioecious species in several unrelated lineages of plants and animals.

Pathogens face numerous challenges to persist in hosts with low or unpredictable population densities. Strategies include horizontal transmission, such as by the production of propagules that persist in the environment, and vertical transmission from adults to offspring. While many pathogens are capable of horizontal and vertical transmission little is known of their relative roles under realistic conditions of changing population densities. Insect baculoviruses can be transmitted both horizontally and vertically, although much of the work on baculovirus transmission has focussed on horizontal transmission that can be effective at high host densities. Here, we examine the prevalence of a vertically-transmitted, covert infection of nucleopolyhedrovirus (NPV) in field populations of the African armyworm, Spodoptera exempta, in Tanzania. African armyworm is a major pest of graminaceous crops in Africa and despite its migratory nature and boom and bust dynamics, NPV epizootics are common and can be intense at the end of the multi-generation armyworm season. We found that virtually all the insects collected in the field were positive for S. exempta NPV (SpexNPV) DNA and 60% of these insects had transcriptionally active virus. This suggests that SpexNPV is transmitted vertically at extremely high levels in field populations of S. exempta and can maintain a persistent infection without obvious symptoms. Similarly high levels of virus DNA and RNA were detected in a S. exempta colony that had been maintained in continuous culture for 5 years. This study provides an insight into mechanisms of pathogen persistence in migratory populations where hosts are unpredictable and indicates that covert infection may be more common and more relevant in disease dynamics of insects than had previously been thought.

Quantifying the importance of pollination intensity and nutrient availability in influencing phenotypic selection on floral traits is an essential step to understanding floral evolutionary responses in complex environments. We quantified phenotypic selection on four floral traits (flowering start date, angle between adjacent flowers, corolla size and number of flowers) in Spiranthes sinensis by manipulating both pollination intensity and N–P–K nutrient availability under a factorial design: pollination intensity (low, medium and high levels, by manipulating the number of days the flowers were open to insect pollination) × N–P–K nutrient addition (low and high, representing natural nutrient levels and nutrient addition, respectively). There was an interactive effect of pollination intensity and nutrient availability on directional selection on corolla size. Selection for larger corolla size through female fitness was observed at medium and low pollination intensities. Selection for larger corolla size through pollen removal was observed in the treatment combining of low level of pollination intensity and natural nutrient levels. Selection for a greater number of flowers was observed in all treatment combinations through both female fitness and pollen removal functions. The results demonstrated that pollination intensity and nutrient availability influenced the opportunity for selection. The opportunity for selection increased in the low level of pollination intensity treatment, but high nutrient addition treatment reduced it. Our study suggests the context-dependence of natural selection in driving floral evolution and emphasizes the need for more studies with a combined focus on abiotic and biotic factors.

Cognitive and sensory abilities are vital in affecting survival under predation risk, leading to selection on brain anatomy. However, how exactly predation and brain evolution are linked has not yet been resolved, as current empirical evidence is inconclusive. This may be due to predation pressure having different effects across life stages and/or due to confounding factors in ecological comparisons of predation pressure. Here, we used adult guppies (Poecilia reticulata) to experimentally test how direct predation during adulthood would impact the relative brain size and brain anatomy of surviving individuals to examine if predators selectively remove individuals with specific brain morphology. To this end, we compared fish surviving predation to control fish, which were exposed to visual and olfactory predator cues but could not be predated on. We found that predation impacted the relative size of female brains. However, this effect was dependent on body size, as larger female survivors showed relatively larger brains, while smaller survivors showed relatively smaller brains when compared to control females. We found no differences in male relative brain size between survivors and controls, nor for any specific relative brain region sizes for either sex. Our results corroborate the important, yet complex, role of predation as an important driver of variation in brain size.