The role of variation and plasticity in parental care during the adaptive radiation of three-spine sticklebacks

Divergence in Reproductive Behaviors Is Associated with the Evolutionary Loss of Parental Care

AbstractThe mechanisms underlying the divergence of reproductive strategies between closely related species are still poorly understood. Additionally, it is unclear which selective factors drive the evolution of reproductive behavioral variation and how these traits coevolve, particularly during early divergence. To address these questions, we quantified behavioral differences in a recently diverged pair of Nova Scotian three-spined stickleback (Gasterosteus aculeatus) populations, which vary in parental care, with one population displaying paternal care and the other lacking this. We compared both populations, and a full reciprocal F1 hybrid cross, across four major reproductive stages: territoriality, nesting, courtship, and parenting. We identified significant divergence in a suite of heritable behaviors. Importantly, F1 hybrids exhibited a mix of behavioral patterns, some of which suggest sex linkage. This system offers fresh insights into the coevolutionary dynamics of reproductive behaviors during early divergence and offers support for the hypothesis that coevolutionary feedback between sexual selection and parental care can drive rapid evolution of reproductive strategies.

Biological Links between Personality and Plasticity: Testing Some Alternative Hypotheses

AbstractWhen organisms respond behaviorally to a stimulus, they exhibit plasticity, but some individuals respond to the same stimulus consistently differently than others, thereby also exhibiting personality differences. Parent house sparrows express individual differences in how often they feed offspring and how that feeding rate changes with nestling age. Mean feeding rate and its slope with respect to nestling age were positively correlated at median nestling ages but not at hatching, indicating that individuality is primarily in plasticity. Individual differences could arise because of (1) interactions between environmental variables, (2) differences in underlying state or "quality," or (3) differences in the ability to update cues of changing nestling demand. Individual slopes were modestly repeatable across breeding attempts, hinting at the likely action of additional environmental variables, but only brood size was important. I also found few correlates suggesting quality differences. I used short-term brood size manipulations at two nestling ages to test divergent predictions between the three hypotheses. The pattern of correlations between response to the manipulation and individual slope did not fit any single hypothesis. Patterns of sparrow parental care reveal that personality and plasticity are not cleanly separable, and their biology is likely intertwined. New thinking may be needed about the factors parents use in decisions about care and the relevant fitness consequences.

Predator-induced transgenerational plasticity of parental care behaviour in male three-spined stickleback fish across two generations

Parental care is a critical determinant of offspring fitness, and parents adjust their care in response to ecological challenges, including predation risk. The experiences of both mothers and fathers can influence phenotypes of future generations (transgenerational plasticity). If it is adaptive for parents to alter parental care in response to predation risk, then we expect F1 and F2 offspring who receive transgenerational cues of predation risk to shift their parental care behaviour if these ancestral cues reliably predict a similarly risky environment as their F0 parents. Here, we used three-spined sticklebacks (Gasterosteus aculeatus) to understand how paternal exposure to predation risk prior to mating alters reproductive traits and parental care behaviour in unexposed F1 sons and F2 grandsons. Sons of predator-exposed fathers took more attempts to mate than sons of control fathers. F1 sons and F2 grandsons with two (maternal and paternal) predator-exposed grandfathers shifted their paternal care (fanning) behaviour in strikingly similar ways: they fanned less initially, but fanned more near egg hatching. This shift in fanning behaviour matches shifts observed in response to direct exposure to predation risk, suggesting a highly conserved response to pre-fertilization predator exposure that persists from the F0 to the F1 and F2 generations.

Male reproductive adjustments to an introduced nest predator

Nest predation has a large impact on reproductive success in many taxa. Defending offspring from would-be predators can also be energetically and physiologically costly for parents. Thus, to maximize their reproductive payoffs, individuals should adjust their reproductive behaviors in relation to the presence of nest predators. However, effects of nest predator presence on parental behaviors across multiple reproductive contexts remain poorly understood, particularly in non-avian taxa. We ran a series of experiments to test how the presence of an egg predator, the invasive rockpool shrimp, Palaemon elegans, influences male reproductive decisions and egg survival in a species of fish with exclusive paternal care, the three-spined stickleback, Gasterosteus aculeatus. We found that, in the presence of shrimp, male sticklebacks were less likely to build a nest, invested less in territory defense against an intruder, and tended to fan eggs in their nest less and in shorter bouts, but did not alter their investment in courtship behavior. The predator’s presence also did not affect egg survival rates, suggesting that males effectively defended their brood from the shrimp. These results show that reproducing individuals can be highly responsive to the presence of nest predators and adjust their behavioral decisions accordingly across a suite of reproductive contexts.

Habitat fragmentation induces rapid divergence of migratory and isolated sticklebacks

The adaptive capacity of many organisms is seriously challenged by human-imposed environmental change, which currently happens at unprecedented rates and magnitudes. For migratory fish, habitat fragmentation is a major challenge that can compromise their survival and reproduction. Therefore, it is important to study if fish populations can adapt to such modifications of their habitat. Here, we study whether originally anadromous three-spined stickleback populations (Gasterosteus aculeatus; “migrants”) changed in behavior and morphology in response to human-induced isolation. We made use of a natural field-experiment, where the construction of pumping stations and sluices in the 1970s unintendedly created replicates of land-locked stickleback populations (“resident”) in the Netherlands. For two years, we systematically tested populations of residents and migrants for differences in morphology and behavioral traits (activity, aggressiveness, exploration, boldness, and shoaling) in lab-based assays. We detected differences between migrant and resident populations in virtually all phenotypic traits studied: compared with the ancestral migrants, residents were smaller in size, had fewer and smaller plates and were significantly more active, aggressive, exploratory and bolder, and shoaled less. Despite large ecological differences between 2018 and 2019, results were largely consistent across the two years. Our study shows that human-induced environmental change has led to the rapid and consistent morphological and behavioral divergence of stickleback populations in about 50 generations. Such changes may be adaptive but this remains to be tested.

Paternal care effects outweigh gamete-mediated and personal environment effects during the transgenerational estimation of risk in fathead minnows

BACKGROUND

Individuals can estimate risk by integrating prenatal with postnatal and personal information, but the relative importance of different information sources during the transgenerational response is unclear. The estimated level of risk can be tested using the cognitive rule of risk allocation, which postulates that under consistent high-risk, antipredator efforts should decrease so that individual metabolic requirements can be satisfied. Here we conduct a comprehensive study on transgenerational risk transmission by testing whether risk allocation occurs across 12 treatments that consist of different maternal, paternal, parental care (including cross-fostering) and offspring risk environment combinations in the fathead minnow Pimephales promelas, a small cyprinid fish with alloparental care. In each risk environment, we manipulated perceived risk by continuously exposing individuals from birth onwards to conspecific alarm cues or a control water treatment. Using 2810 1-month old individuals, we then estimated shoaling behaviour prior to and subsequent to a novel mechanical predator disturbance.

RESULTS

Overall, shoals estimating risk to be high were denser during the prestimulus period, and, following the risk allocation hypothesis, resumed normal shoaling densities faster following the disturbance. Treatments involving parental care consistently induced densest shoals and greatest levels of risk allocation. Although prenatal risk environments did not relate to paternal care intensity, greater care intensity induced more risk allocation when parents provided care for their own offspring as opposed to those that cross-fostered fry. In the absence of care, parental effects on shoaling density were relatively weak and personal environments modulated risk allocation only when parental risk was low.

CONCLUSIONS

Our study highlights the high relative importance of parental care as opposed to other information sources, and its function as a mechanism underlying transgenerational risk transmission.

Larval environmental conditions influence plasticity in resource use by adults in the burying beetle, Nicrophorus vespilloides

Recent studies have shown that intraspecific patterns of phenotypic plasticity can mirror patterns of evolutionary diversification among species. This appears to be the case in Nicrophorus beetles. Within species, body size is positively correlated with the size of carrion used to provision larvae and parental performance. Likewise, among species, variation in body size influences whether species exploit smaller or larger carrion and the extent to which larvae depend on parental care. However, it is unclear whether developmental plasticity in response to carcass size, parental care, or both underlie transitions to new carcass niches. We examined this by testing whether variation in the conditions experienced by Nicrophorus vespilloides larvae influenced their ability to breed efficiently upon differently sized carcasses as adults. We found that the conditions experienced by larvae during development played a critical role in determining their ability to use large carcasses effectively as adults. Specifically, individuals that developed with parental care and on large carcasses were best able to convert the resources on a large carcass into offspring when breeding themselves. Our results suggest that parentally induced plasticity can be important in the initial stages of niche expansion.

Contextual behavioural plasticity in Italian agile frog (Rana latastei) tadpoles exposed to native and alien predator cues

Predation is a strong driver for the evolution of prey behaviour. To properly assess the actual risk of predation, anuran tadpoles mostly rely on water-borne chemical cues, and their ability to evaluate environmental information is even more crucial when potential predators consist of unknown alien species. Behavioural plasticity - that is, the capacity to express changes in behaviour in response to different environmental stimuli - is crucial to cope with predation risk. We explored the defensive behaviour of Italian agile frog (Rana latastei) tadpoles when exposed to the chemical cues of two predator species, one native (dragonfly larvae) and one alien (red swamp crayfish). Firstly, we observed whether a plastic life history trait (i.e. hatching time) might be affected by native predatory cues. Secondly, we recorded a suite of behavioural responses (activity level, lateralization and sinuosity) to each cue. For assessing lateralization and sinuosity, we developed a C++ code for the automatic analysis of digitally recorded tadpole tracks. Hatching time seemed not to be affected by the potential risk of predation, while both predator species and diet affected tadpoles' defensive behaviour. Tadpoles responded to a predator threat by two main defensive strategies: freezing and 'zig-zagging'. While the first behaviour had previously been reported, the analysis of individual trajectories indicated that tadpoles can also increase path complexity, probably to prevent predators from anticipating their location. We also recorded a decrease in lateralization intensity, which suggests that under predation risk, tadpoles tend to scrutinize the surrounding environment equally on both sides.