Diversity and composition of mixed-ploidy unisexual salamander assemblages reflect the key influence of host species.

Understanding processes that govern and sustain biological diversity is a central goal of community ecology. Unisexual complexes, where reproduction depends on sperm from males of one or more bisexual host species, are rare and the processes driving their diversity and structure remain poorly understood. Unisexual Ambystoma salamanders produce distinct biotypes ('genomotypes') depending on which bisexual species they 'steal' sperm from. This reproductive mode should generate distinct assemblages depending on the locally available bisexual host species. Yet, how availability and relative abundance of multiple bisexual hosts influences composition and diversity of natural unisexual assemblages at local or regional scales remains unknown. We hypothesize that host identity most directly drives local assemblage composition, with host variation associated with increased beta and gamma diversity within unisexuals. We collected genetic samples from Ambystoma salamanders across Pelee Island, Ontario, Canada (2015-2022). Two host species were identified (A. texanum and A. laterale) with nine sites having a single host and one site having both. Unisexual assemblages were grouped into four clusters by similarity, with host identity being a key determinant. Gamma diversity increased as a result of distinct host-specific assemblages forming at different sites on the island (i.e., high beta diversity). Assemblage composition, but not diversity, was correlated with relative host abundance, which may reflect matching niche requirements between host and unisexual forms they produce. Our results demonstrate that diversity and structure of unisexual assemblages are clearly shaped by their host(s) and such systems may serve as models for studying how biotic interactions shape ecological communities.

The evolution and ecology of multiple antipredator defences.

Prey seldom rely on a single type of antipredator defence, often using multiple defences to avoid predation. In many cases, selection in different contexts may favour the evolution of multiple defences in a prey. However, a prey may use multiple defences to protect itself during a single predator encounter. Such "defence portfolios" that defend prey against a single instance of predation are distributed across and within successive stages of the predation sequence (encounter, detection, identification, approach (attack), subjugation and consumption). We contend that at present, our understanding of defence portfolio evolution is incomplete, and seen from the fragmentary perspective of specific sensory systems (e.g., visual) or specific types of defences (especially aposematism). In this review, we aim to build a comprehensive framework for conceptualizing the evolution of multiple prey defences, beginning with hypotheses for the evolution of multiple defences in general, and defence portfolios in particular. We then examine idealized models of resource trade-offs and functional interactions between traits, along with evidence supporting them. We find that defence portfolios are constrained by resource allocation to other aspects of life history, as well as functional incompatibilities between different defences. We also find that selection is likely to favour combinations of defences that have synergistic effects on predator behaviour and prey survival. Next, we examine specific aspects of prey ecology, genetics and development, and predator cognition that modify the predictions of current hypotheses or introduce competing hypotheses. We outline schema for gathering data on the distribution of prey defences across species and geography, determining how multiple defences are produced, and testing the proximate mechanisms by which multiple prey defences impact predator behaviour. Adopting these approaches will strengthen our understanding of multiple defensive strategies.

Boldness, movement and exploration tendency in round goby (Neogobius melanostomus) in Southern Ontario.

Invasive species have the potential to damage ecosystems outside their native range. At an invasion front, individuals are faced with the unfamiliar conditions of a novel environment. Therefore, certain behavioural traits such as boldness and movement likely play a role in invasion ecology. If behavioural traits of this kind are influenced by differing selection pressures between demographic groups of the same species, this could have broad implications for the management of expanding invasion fronts. To determine whether the invasive round goby (Neogobius melanostomus, Pallas, 1814) exhibits sex- and habitat-based differences in boldness and movement across the invasion front, the authors assessed individual movement and exploration tendency under controlled lab settings using video analysis in a behavioural assay. N. melanostomus from lakes tended to be bolder than those from streams, and females tended to be bolder than males. This study provides evidence for sex- and habitat-based differences in behaviour in this globally invasive species that the authors hope will assist in forming the foundation for contextually appropriate management strategies.

Density-Dependent Cannibalism in Dragonfly Nymphs (Odonata: Anisoptera) Overwintering in Temperate Freshwater Ponds.

Density-dependent mortality by predation and cannibalism has been observed in aquatic insects such as dragonflies in response to shrinking habitat caused by summer drought. Winter conditions might also reduce the amount of livable habitat in temperate ponds and could augment rates of cannibalism. We hypothesized that cannibalism in dragonfly nymphs would increase in winter due to a seasonal decrease in available habitat caused by stratified lower oxygen levels leading to increased nymph density around pond edges. To determine whether cannibalism in nymphs is density-dependent and size-dependent (i.e., with smaller nymphs consumed) we experimentally manipulated nymph density in aquaria. To evaluate whether these patterns are observed in nature during the winter, we conducted field surveys for nymphs in two ponds across the fall and winter seasons. When nymphs were housed at different densities for 24 h, cannibalism was density-dependent, and only smaller nymphs were preyed upon. Our field surveys found that fewer nymphs were caught in the late winter sampling period (mixed-effects model, P < 0.001), and that these were larger than nymphs caught in the fall, although both patterns were restricted to the deeper pond (P < 0.05). Our results were consistent with the process we hypothesized, and the observed reduction in dissolved oxygen at the bottom of the deeper pond. The lack of significant changes to the relative abundance and size of nymphs in the shallower pond reveals that differences in pond characteristics can influence the degree to which winter conditions induce density-dependent cannibalism among dragonfly nymphs.

Increasing availability of palatable prey induces predator-dependence and increases predation on unpalatable prey.

Understanding the factors governing predation remains a top priority in ecology. Using a dragonfly nymph-tadpole system, we experimentally varied predator density, prey density, and prey species ratio to investigate: (i) whether predator interference varies between prey types that differ in palatability, (ii) whether adding alternate prey influences the magnitude of predator interference, and (iii) whether patterns of prey selection vary according to the predictions of optimal diet theory. In single-prey foraging trials, predation of palatable leopard frog tadpoles was limited by prey availability and predator interference, whereas predation of unpalatable toad tadpoles was limited by handling time. Adding unpalatable prey did not affect the predator's kill rate of palatable prey, but the presence of palatable prey increased the influence of predator density on the kill rate of unpalatable prey and reduced unpalatable prey handling time. Prey selection did not change with shifts in the relative abundance of prey types. Instead, predators selected easy-to-capture unpalatable prey at low total densities and harder-to-capture palatable prey at high densities. These results improve our understanding of generalist predation in communities with mobile prey, and illustrate that characteristics of the prey types involved govern the extent to which alternate prey influence the predator's kill rate.

Threat of predation alters aggressive interactions among spotted salamander (Ambystoma maculatum) larvae.

Intraspecific aggression represents a major source of mortality for many animals and is often experienced alongside the threat of predation. The presence of predators can strongly influence ecological systems both directly by consuming prey and indirectly by altering prey behavior or habitat use. As such, the threat of attack by higher level predators may strongly influence agonistic interactions among conspecifics via nonconsumptive (e.g., behaviorally mediated) predator effects. We sought to investigate these interactions experimentally using larval salamanders (Ambystoma maculatum) as prey and dragonfly nymphs (Anax junius) as predators. Specifically, we quantified salamander behavioral responses to perceived predation risk (PPR) from dragonfly nymphs and determined the degree to which PPR influenced intraspecific aggression (i.e., intraspecific biting and cannibalism) among prey. This included examining the effects of predator exposure on the magnitude of intraspecific biting (i.e., extent of tail damage) and the resulting change in performance (i.e., burst swim speed). Salamander larvae responded to PPR by reducing activity and feeding, but did not increase refuge use. Predator exposure did not significantly influence overall survival; however, the pattern of survival differed among treatments. Larvae exposed to PPR experienced less tail damage from conspecifics, and maximum burst swim speed declined as tail damage became more extensive. Thus, escape ability was more strongly compromised by intraspecific aggression occurring in the absence of predation risk. We conclude that multitrophic indirect effects may importantly modulate intraspecific aggression and should be considered when evaluating the effects of intraspecific competition.

Spatial arrangement of prey affects the shape of ratio-dependent functional response in strongly antagonistic predators.

Predators play a key role in shaping natural ecosystems, and understanding the factors that influence a predator's kill rate is central to predicting predator-prey dynamics. While prey density has a well-established effect on predation, it is increasingly apparent that predator density also can critically influence predator kill rates. The effects of both prey and predator density on the functional response will, however, be determined in part by their distribution on the landscape. To examine this complex relationship we experimentally manipulated prey density, predator density, and prey distribution using a tadpole (prey)-dragonfly nymph (predator) system. Predation was strongly ratio-dependent irrespective of prey distribution, but the shape of the functional response changed from hyperbolic to sigmoidal when prey were clumped in space. This sigmoidal functional response reflected a relatively strong negative effect of predator interference on kill rates at low prey: predator ratios when prey were clumped. Prey aggregation also appeared to promote stabilizing density-dependent intraguild predation in our system. We conclude that systems with highly antagonistic predators and patchily distributed prey are more likely to experience stable dynamics, and that our understanding of the functional response will be improved by research that examines directly the mechanisms generating interference.

Eyespots.

Skelhorn et al. introduce eyespots the circular markings resembling vertebrate eyes found on many animals.

The evolution of peer review as a basis for scientific publication: directional selection towards a robust discipline?

Peer review is pivotal to science and academia, as it represents a widely accepted strategy for ensuring quality control in scientific research. Yet, the peer-review system is poorly adapted to recent changes in the discipline and current societal needs. We provide historical context for the cultural lag that governs peer review that has eventually led to the system's current structural weaknesses (voluntary review, unstandardized review criteria, decentralized process). We argue that some current attempts to upgrade or otherwise modify the peer-review system are merely sticking-plaster solutions to these fundamental flaws, and therefore are unlikely to resolve them in the long term. We claim that for peer review to be relevant, effective, and contemporary with today's publishing demands across scientific disciplines, its main components need to be redesigned. We propose directional changes that are likely to improve the quality, rigour, and timeliness of peer review, and thereby ensure that this critical process serves the community it was created for.