When the optimal phenotype differs among environments, adaptive phenotypic plasticity can evolve unless constraints impede such evolution. Costs and limits of plasticity have been proposed as ...important constraints on the evolution of plasticity, yet confusion exists over their distinction. We attempt to clarify these concepts by reviewing their categorization and measurement, highlighting how costs and limits are defined in different currencies (and may describe the same phenomenon). Conclusions from studies that measure the costs of plasticity have been equivocal, but we caution that these conclusions may be premature owing to a potentially common correlation between environment-specific trait values and the magnitude of trait plasticities (i.e. multi-collinearity) that results in imprecise and/or biased estimates of the costs. Meanwhile, our understanding of the limits of plasticity, and how they may be underlain by the costs of plasticity, is still in its infancy. Based on our re-evaluation of these constraints, we discuss areas for future research.
Seed dormancy, by controlling the timing of germination, can strongly affect plant survival. The kind of seed dormancy, therefore, can influence both population and species‐level processes such as ...colonization, adaptation, speciation, and extinction. We used a dataset comprising over 14 000 taxa in 318 families across the seed plants to test hypotheses on the evolution of different kinds of seed dormancy and their association with lineage diversification. We found morphophysiological dormancy to be the most likely ancestral state of seed plants, suggesting that physiologically regulated dormancy in response to environmental cues was present at the origin of seed plants. Additionally, we found that physiological dormancy (PD), once disassociated from morphological dormancy, acted as an ‘evolutionary hub’ from which other dormancy classes evolved, and that it was associated with higher rates of lineage diversification via higher speciation rates. The environmental sensitivity provided by dormancy in general, and by PD in particular, appears to be a key trait in the diversification of seed plants.
Excluding insects, hermaphroditism occurs in about one-third of animal species, providing numerous opportunities for the evolution of selfing. Here we provide an overview of reproductive traits in ...hermaphroditic animal species, review the distribution of selfing rates in animals, and test for ecological correlates of selfing. Our dataset (1342 selfing-rate estimates for 142 species) is 97% based on estimates derived from the analysis of population structure (FIS-estimates) using genetic markers. The distribution of selfing is slightly 𝗨-shaped and differs significantly from the more strongly 𝗨-shaped plant distribution with 47% of animal t-estimates being intermediate (falling between 0.2 and 0.8) compared to 42% for plants. The influence of several factors on the distribution of selfing rates was explored (e.g., number of populations studied per species, habitat, coloniality, sessility, or fertilization type), none of which significantly affect the distribution. Our results suggest that genetic forces might contribute to the evolution of self-fertilization to the same extent in animals and plants, although the high proportion of intermediate outcrossing suggests a significant role of ecological factors (e.g., reproductive assurance) in animals. However, we caution that the distribution of selfing rates in animals is affected by various factors that might bias FIS-estimates, including phylogenetic underrepresentation of highly selfing and outcrossing species, various genotyping errors (e.g., null alleles) and inbreeding depression. This highlights the necessity of obtaining better estimates of selfing for hermaphroditic animals, such as genotyping progeny arrays, as in plants.
The scope of Baker's law Pannell, John R.; Auld, Josh R.; Brandvain, Yaniv ...
New phytologist,
November 2015, Letnik:
208, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Baker's law refers to the tendency for species that establish on islands by long-distance dispersal to show an increased capacity for self-fertilization because of the advantage of self-compatibility ...when colonizing new habitat. Despite its intuitive appeal and broad empirical support, it has received substantial criticism over the years since it was proclaimed in the 1950s, not least because it seemed to be contradicted by the high frequency of dioecy on islands. Recent theoretical work has again questioned the generality and scope of Baker's law. Here, we attempt to discern where the idea is useful to apply and where it is not. We conclude that several of the perceived problems with Baker's law fall away when a narrower perspective is adopted on how it should be circumscribed. We emphasize that Baker's law should be read in terms of an enrichment of a capacity for uniparental reproduction in colonizing situations, rather than of high selfing rates. We suggest that Baker's law might be tested in four different contexts, which set the breadth of its scope: the colonization of oceanic islands, metapopulation dynamics with recurrent colonization, range expansions with recurrent colonization, and colonization through species invasions.
Because establishing a new population often depends critically on finding mates, individuals capable of uniparental reproduction may have a colonization advantage. Accordingly, there should be an ...over-representation of colonizing species in which individuals can reproduce without a mate, particularly in isolated locales such as oceanic islands. Despite the intuitive appeal of this colonization filter hypothesis (known as Baker’s law), more than six decades of analyses have yielded mixed findings.
We assembled a dataset of island and mainland plant breeding systems, focusing on the presence or absence of self-incompatibility. Because this trait enforces outcrossing and is unlikely to re-evolve on short timescales if it is lost, breeding system is especially likely to reflect the colonization filter.
We found significantly more self-compatible species on islands than mainlands across a sample of > 1500 species from three widely distributed flowering plant families (Asteraceae, Brassicaceae and Solanaceae). Overall, 66% of island species were self-compatible, compared with 41% of mainland species.
Our results demonstrate that the presence or absence of self-incompatibility has strong explanatory power for plant geographical patterns. Island floras around the world thus reflect the role of a key reproductive trait in filtering potential colonizing species in these three plant families.
The length of the reproductive life span, along with the number/frequency/magnitude of reproductive events, quantifies an individual's potential contribution to the next generation. By examining ...reproductive life span, and distinguishing it from somatic life span, we gain insight into critical aspects of an individual's potential fitness as well as reproductive and somatic senescence. Additionally, differentiating somatic and reproductive life spans can provide insight into the existence of a post‐reproductive period and factors that shape its duration. Given the known importance of diet and mating system on resource allocation, I reared individual freshwater snails (Physa acuta) from 22 full‐sib families under a 2 × 2 factorial design that crossed mate availability (available outcrossing or not selfing) and diet (Spirulina or lettuce) and quantified aspects of the entire life history enabling me to distinguish reproductive and somatic life spans, determine the total number of reproductive events, and evaluate how the reproductive rate changes with age. Overall, mated snails experienced shorter reproductive and somatic life spans; a diet of Spirulina also shortened both reproductive and somatic life spans. A post‐reproductive period existed in all conditions; its duration was proportional to somatic but not reproductive life span. I evaluate several hypotheses for the existence and duration of the post‐reproductive period, including a novel hypothesis that the post‐reproductive period may result from an increase in reproductive interval with age. I conclude that the post‐reproductive period may be indicative of a randomly timed death occurring as the interval between reproductive events continues to increase. As such, a “post‐reproductive” period can be viewed as a by‐product of a situation where reproductive senescence outpaces somatic senescence.
This is an experimental evaluation of reproductive and post‐reproductive life span in a freshwater snail, exploring the effects of diet and mating system on fundamental aspects of the life history. Snails reared on a higher quality diet or allowed access to a mating partner suffered a reduced reproductive life span. A post‐reproductive period exists under all conditions and its existence is discussed.
Reproductive performance is often age-dependent, showing patterns of improvement and/or senescence as well as trade-offs with other traits throughout the lifespan. High levels of extrinsic mortality ...(e.g., from predators) have been shown to sometimes, but not always, select for accelerated actuarial senescence in nature and in the lab. Here, we explore the inductive (i.e., plastic) effects of predation risk (i.e., nonlethal exposure to chemical cues from predators) on the reproductive success of freshwater snails (Physa acuta). Snails were reared either in the presence or absence of chemical cues from predatory crayfish and mated early in life or late in life (a 2 × 2 factorial design); we measured egg hatching and early post-hatching survival of their offspring. Both age and predation risk reduced reproductive success, illustrating that predation risk can have a cross-generational effect on the early survival of juveniles. Further, the decline in reproductive success was over three times faster under predation risk compared to the no-predator treatment, an effect that stemmed from a disproportionate, negative effect of predation risk on the post-hatching survival instead of hatching rate. We discuss our results in terms of a hypothesized consequence of elevated stress hormone levels.
Environmental effects on mating system expression are central to understanding mating system evolution in nature. Here, I report the results from a quantitative-genetic experiment aimed at ...understanding the role of predation risk in the expression and evolution of life-history and mating-system traits in a hermaphroditic freshwater snail (Physa acuta). I reared 30 full-sib families in four environments that factorially contrast predation risk and mate availability and measured age/size at first reproduction, growth rate, a morphological defense, and the early survival of outcrossed/selfed eggs that were laid under predator/no-predator conditions. I evaluated the genetic basis of trade-offs among traits and the stability of the G matrix across environments. Mating reduced growth while predation risk increased growth, but the effects of mating were weaker for predator-induced snails and the effects of predation risk were weaker for snails without mates. Predation risk reduced the amount of time that individuals waited before self-fertilizing and reduced inbreeding depression in the offspring. There was a positive among-family relationship between the amount of time that individuals delayed selfing under prédation risk and the magnitude of inbreeding depression. These results highlight several potential roles of enemies in mating-system expression and evolution.
Sexual selection is often quantified using Bateman gradients, which represent sex‐specific regression slopes of reproductive success on mating success and thus describe the expected fitness returns ...from mating more often. Although the analytical framework for Bateman gradients aimed at covering all sexual systems, empirical studies are biased toward separate‐sex organisms, probably because important characteristics of other systems remain incompletely treated. Our synthesis complements the existing Bateman gradient approach with three essential reproductive features of simultaneous hermaphrodites. First, mating in one sex may affect fitness via the opposite sex, for example, through energetic trade‐offs. We integrate cross‐sex selection effects and show how they help characterizing sexually mutualistic versus antagonistic selection. Second, male and female mating successes may be correlated, complicating the interpretation of Bateman gradients. We show how to quantify the impact of this correlation on sexual selection and propose a principal component analysis on male and female mating success to facilitate interpretation. Third, self‐fertilization is accounted for by adding selfed progeny as a separate category of reproductive success to analyses of Bateman gradients. Finally, using a worked example from the snailBiomphalaria glabrata, we illustrate how the extended analytical framework can enhance our understanding of sexual selection in hermaphroditic animals and plants.
The optimal timing for initiating reproduction (i.e., the age at first reproduction) is a critical life history trait describing aspects of an individual’s resource-allocation strategy. Recent ...theoretical and empirical work has demonstrated that this trait is also tied to mating system expression when individuals have the opportunity to reproduce via both self-fertilization and cross-fertilization. A strategy of “delayed selfing” has emerged as a “best of both worlds” arrangement where, in the absence of a mate, an individual will delay reproduction (selfing) to “wait” for a mate. Herein, we extend previously developed predictive optimization models for the timing of reproduction to a situation where organisms can allocate their resources to size-dependent and size-independent defensive strategies to counter the threat of predation. By incorporating inducible defenses into a predictive framework for analyzing life history expression and evolution, we can more accurately evaluate the role that allocation strategy plays in altering the optimal waiting time. We compare our model to previous models and empirical results highlighting that incorporation of inducible defenses into the model broadens the parameter space in which a waiting time is expected and often leads to a predicted waiting time that is longer than in the situation without inducible defenses. In particular, a waiting time is predicted to exist regardless of the strength of inbreeding depression in the population.
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