Brain transcriptome analysis reveals gene expression differences associated with dispersal behaviour between range-front and range-core populations of invasive cane toads in Australia

Understanding the mechanisms underlying rapid adaptation of invasive species in novel environments is key to improving our ability to manage these species. Many invaders demonstrate rapid evolution of behavioural traits involved in range expansion such as locomotor activity, exploration and risk-taking. However, the molecular mechanisms that underpin these changes are poorly understood. In 86 years, invasive cane toads (Rhinella marina) in Australia have drastically expanded their geographic range westward from coastal Queensland to Western Australia. During their range expansion, toads have undergone extensive phenotypic changes, particularly in behaviours that enhance the toads' dispersal ability. Common-garden experiments have shown that some changes in behavioural traits related to dispersal are heritable. However, genetic diversity is greatly reduced across the invasive range due to a strong founder effect, and the genetic basis underlying dispersal-related behavioural changes remains unknown. Here we used RNA-seq to compare the brain transcriptomes of toads from the Hawai'ian source population, as well as three distinct populations from across the Australian invasive range. We found markedly different gene expression profiles between the source population and Australian toads. By contrast, cane toads from across the Australian invasive range had very similar transcriptomic profiles. Yet, key genes with functions putatively related to dispersal behaviour showed differential expression between range-core and range-front populations. These genes could play an important role in the behavioural changes characteristic of range expansion in Australian cane toads.

Electrical signalling on Bt and non-Bt cotton plants under stress by Aphis gossypii

Plants have developed various mechanisms to respond specifically to each biotrophic attack. It has been shown that the electrical signals emitted by plants are associated with herbivory stress responses and can lead to the activation of multiple defences. Bt cotton is a genetically modified pest-resistant plant that produces an insecticide from Bacillus thuringiensis (Bt) to control Lepidopteran species. Surprisingly, there is no study–yet, that characterizes the signalling mechanisms in transgenic cotton plants attacked by non-target insects, such as aphids. In this study, we characterized the production of electrical signals on Bt and non-Bt cotton plants infested with Aphis gossypii and, in addition, we characterized the dispersal behaviour of aphids to correlate this behaviour to plant signalling responses. Electrical signalling of the plants was recorded with an extracellular measurement technique. Impressively, our results showed that both Bt and non-Bt cotton varieties, when attacked by A. gossypii, emitted potential variation-type electrical signals and clearly showed the presence of distinct responses regarding their perception and the behaviour of aphids, with evidence of delay, in terms of signal amount, and almost twice the amount of Cry1F protein was observed on Bt cotton plants at the highest density of insects/plant. We present in our article some hypotheses that are based on plant physiology and insect behaviour to explain the responses found on Bt cotton plants under aphid stress.

Exploratory behaviour, memory and neurogenesis in the social Damaraland mole-rat (Fukomys damarensis)

ABSTRACTBoth exploratory behaviour and spatial memory are important for survival in dispersing animals. Exploratory behaviour is triggered by novel environments and having a better spatial memory of the surroundings provides an adaptive advantage to the animals. Spatial challenges can also affect neurogenesis in the hippocampus by increasing cell proliferation and enhancing survival of young neurons. In social Damaraland mole-rat colonies, the social hierarchy is largely based on body size. Individuals with different social statuses in these colonies display different dispersal behaviours and as behavioural differences have been linked to dispersal behaviour, I investigated exploratory behaviour, memory and hippocampal neurogenesis in wild-captured Damaraland mole-rats. Dispersal behaviour gives rise to differential exploratory behaviour in Damaraland mole-rats; they readily explored in a novel environment but resident, worker mole-rats explored more slowly. In the Y-maze, animals entered the escape hole significantly faster by the second day; however, they did not make fewer wrong turns with successive days of the experiment. Female dispersers did not show any improvement in time to reach the escape hole or the number of wrong turns over the 4 day experimental period. Damaraland male and female dispersers employ different dispersal strategies, and this is evident in their approach to the learning task. Females are less motivated to complete the task, leading to a difference in behaviour, and this has important survival implications for the different sexes. Finally, in the context of memory, adult neurogenesis does not seem to be a good marker in mole-rats as it is generally low and has not been investigated thoroughly enough to determine which and how other factors can influence it in these animals.

Wide dispersal of recently weaned grey seal pups in the Southern North Sea

Grey seals have become an important part of the ecosystem in the southern North Sea over the last 50 years. However, little is known about their spatial utilization of the German North Sea, especially in relation to the dispersal and behaviour of grey seal pups after weaning. We investigated these little-known aspects by recording the movements of 11 grey seal pups born at the largest German colony for 1–9 months after leaving the colony between 2015 and 2017. The individuals moved widely throughout the southern North Sea, including some individuals that moved far along the Danish coast or to Dutch and UK waters. A point process modelling approach revealed that pups increased their distance to Helgoland during the first 70 d at sea. The frequency of inferred foraging behaviour increased until week 7 and decreased afterwards, whereas fast travelling behaviour increased throughout the whole study period. These findings reflect the transition from naive to more experienced pups, with gradual increases in foraging effort, range and efficiency to account for their increasing energy demands for survival and growth. This study provides the first characterization of the dispersal, behaviour, and spatial utilization of recently weaned grey seal pups in the southern North Sea, which profoundly extents our knowledge of an increasingly important top predator in that area.

Dispersal, endosymbiont abundance and fitness-related consequences of inbreeding and outbreeding in a social beetle

Most social species outbreed. However, some have persistent inbreeding with occasional outbreeding, and the decision of the individual regarding whether to stay in the natal group and inbreed or to disperse, with the potential to outbreed, is flexible and may depend on social, genetic and ecological benefits and costs. Few of these factors have been investigated experimentally in these systems. The beetle Coccotrypes dactyliperda Fabricius, 1801 (Scolytidae: Xyloborinae) lives in extended family colonies inside date seeds. The beetles inbreed, but some individuals disperse away from the natal seed and may outbreed. We investigated dispersal behaviour and assessed fitness-related measures in inbred and outbred offspring, in addition to the relative abundance of two endosymbionts. We predicted inbred offspring to have higher fitness-related measures and a reduced tendency to disperse than outbred offspring, owing to fitness benefits of cooperation within the colony, whereas increased endosymbiont abundance will promote dispersal of their hosts, thus enhancing their own spread in the population. Dispersing beetles were more active than ones that remained in the natal seed. As predicted, fewer inbred offspring dispersed than outbred offspring, but they matured and dispersed earlier. Fitness-related measures of inbred mothers were either lower (number of offspring) or not different (body mass) from those of outbred mothers. Inbred dispersers had greater amounts of Wolbachia, suggesting a role in dispersal. The results support the hypothesis that inbred females reduce dispersal and that early maturation and dispersal are likely to be benefits of increased cooperation in brood care.

Dispersal behaviour as the outcome and trigger of multilevel selection in a social spider

The facultatively social spider Anelosimus studiosus offers a unique opportunity for understanding how multilevel selection acts in natural populations. However, the importance of previous empirical studies are shaded by a conceptual debate about whether colony-level selection is truly present in these populations or not. Here we introduce a detailed individual based model, where practically all assumptions are supported by empirical data. The only element of the female A. studiosus life cycle missing from the literature is how maturing female spiders decide whether to disperse. This behavioural component we estimate with evolutionary simulations. This model is able to recapitulate the characteristic size and composition distributions of natural populations in different environments. The evolutionary simulations revealed that the optimal dispersal behaviour of a maturing female varies both with her ecological environment and behavioural phenotype. This finding is open for straightforward empirical testing. In agreement with empirical findings we have established parameter ranges where the population is prone to extinction without multiple-female nests. We propose that the dispersal behaviour of individuals is both the result and the prerequisite of multilevel selection in this species.