Jonathan Henshaw

Jonathan Henshaw
University of Freiburg | Albert-Ludwigs-Universität Freiburg · Institute of Biology I

PhD

About

27
Publications
12,486
Reads
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319
Citations
Education
February 2013 - December 2017
Australian National University
Field of study
  • Evolutionary biology

Publications

Publications (27)
Article
Full-text available
Males and females are defined by the relative size of their gametes (anisogamy), but secondary sexual dimorphism in fertilization, parental investment and mating competition is widespread and often remarkably stable over evolutionary timescales. Recent theory has clarified the causal connections between anisogamy and the most prevalent differences...
Article
Full-text available
The consequences of natural selection can be understood from a purely statistical perspective. In contrast, an explicitly causal approach is required to understand why trait values covary with fitness. In particular, key evolutionary constructs like sexual selection, fecundity selection, and so on, are best understood as selection via particular fi...
Article
Costly signalling theory is based on the idea that individuals may signal their quality to potential mates and that the signal's costliness plays a crucial role in maintaining information content ('honesty') over evolutionary time. Whereas costly signals have traditionally been described as 'handicaps', here we present mathematical results that mot...
Article
The year 2021 marks the 150th anniversary of the publication of Charles Darwin’s extraordinary book The Descent of Man and Selection in Relation to Sex. Here, we review the history and impact of a single profound insight from The Descent of Man: that, in some few species, females rather than males compete for access to mates. In other words, these...
Article
Full-text available
Keywords: aggression biparental care cichlid fish mate removal parental investment sex role territoriality In many animal systems, the defence of a territory or nest coincides with the defence of offspring, and it is often unclear whether the defence behaviour exists for the purpose of offspring protection, territory protection or a combination of...
Article
Full-text available
Ecologists and evolutionary biologists are well aware that natural and sexual selection do not operate on traits in isolation, but instead act on combinations of traits. This long-recognized and pervasive phenomenon is known as multivariate selection, or—in the particular case where it favours correlations between interacting traits—correlational s...
Article
Natural selection is a key mechanism of evolution, which results from the differential reproduction of individuals due to differences in phenotype. We describe fecundity selection on 13 anthropometric traits in a sample of 4000–10,000 of Estonian girls, who were born between 1937 and 1962 and measured at around 13 years of age. Direct selection fav...
Article
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Background: Raising unrelated offspring is typically wasteful of parental resources and so individuals are expected to reduce or maintain low levels of parental effort when their parentage is low. This can involve facultative, flexible adjustments of parental care to cues of lost parentage in the current brood, stabilizing selection for a low leve...
Article
Full-text available
The bizarre elaboration of sexually selected traits like the peacock's tail was a puzzle to Charles Darwin and his 19th century followers. Ronald A. Fisher crafted an ingenious solution in the 1930s, positing that female preferences would become genetically correlated with preferred traits due to non‐random mating. These genetic correlations would...
Article
Full-text available
Sexually transmitted infections (STIs) often lower their host’s future reproductive success by inducing sterility. Females can minimise the reproductive cost of infection by plastically increasing their current reproductive effort (i.e. terminal investment) before they become sterile. In polyandrous systems, long-term female survival or fecundity i...
Chapter
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Article
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Background In socially monogamous species, reproduction is not always confined to paired males and females. Extra-pair males commonly also reproduce with paired females, which is traditionally thought to be costly to the females’ social partners. However, we suggest that when the relatedness between reproducing individuals is considered, cuckolded...
Article
Full-text available
Extra‐pair paternity within socially monogamous mating systems is well‐studied in birds and mammals but rather neglected in other animal taxa. In fishes, social monogamy has evolved several times but few studies have investigated the extent to which pair‐bonded male fish lose fertilizations to cuckolders and gain extra‐pair fertilizations themselve...
Article
Full-text available
Natural selection operates via fitness components like mating success, fecundity and longevity, which can be understood as intermediaries in the causal process linking traits to fitness. Sexual selection occurs when traits influence mating or fertilisation success, which, in turn, influences fitness. We show how to quantify both these steps in a si...
Article
Full-text available
When mates are encountered sequentially, each encounter involves a decision whether to reject the current suitor, and risk not finding a better mate, or to accept them despite their flaws. I provide a flexible framework for modelling optimal choosiness when mate encounters occur unpredictably in time. The model allows for temporal variation in the...
Article
Full-text available
Sedentary broadcast-spawning marine invertebrates, which release both eggs and sperm into the water for fertilization, are of special interest for sexual selection studies. They provide unique insight into the early stages of the evolutionary succession leading to the often-intense operation of both pre- and post-mating sexual selection in mobile g...
Chapter
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Article
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Spatial and temporal variation in environmental factors and the social setting can help to maintain genetic variation in sexually selected traits if it affects the strength of directional selection. A key social parameter which affects the intensity of, and sometimes predicts the response to, mating competition is the operational sex ratio (OSR; ra...
Article
Full-text available
Lande and Arnold's approach to quantifying natural selection has become a standard tool in evolutionary biology due to its simplicity and generality. It treats linear and nonlinear selection in two separate frameworks, generating coefficients of selection (e.g. linear and quadratic selection gradients) that are not directly comparable. Due to this...
Thesis
To understand how mating systems evolve, we depend on both (i) theoretical explanations and predictions, supported by mathematical modelling, and (ii) quantitative tools to test predictions rigorously. This thesis is divided equally between these two aims. The first three papers explore the evolution of mating systems using analytic and simulation...
Article
Full-text available
Sexual selection is a cornerstone of evolutionary theory, but measuring it has proved surprisingly difficult and controversial. Various proxy measures-e.g., the Bateman gradient and the opportunity for sexual selection-are widely used in empirical studies. However, we do not know how reliably these measures predict the strength of sexual selection...
Article
Full-text available
The parents’ phenotype, or the environment they create for their young, can have longlasting effects on their offspring, with profound evolutionary consequences. Yet, virtually no work has considered how such parental effects might change the adaptive value of behavioural traits expressed by offspring upon reaching adulthood. To address this proble...
Article
Full-text available
Simultaneous hermaphroditism is predicted to be unstable at high mating rates given an associated increase in sperm competition. The existence of reciprocal egg trading, which requires both hermaphroditism and high mating rates to evolve, is consequently hard to explain. We show using mathematical models that the presence of a trading economy creat...
Article
Full-text available
Egg trading—the alternating exchange of egg parcels during mating by simul- taneous hermaphrodites—is one of the best-documented examples of reciprocity between non-relatives. By offering eggs only to partners who reciprocate, traders increase their repro- ductive success in the male role, but at a potential cost of delaying or reducing fertilisati...
Article
Full-text available
Within and across taxa, there is much variation in the mode of fertilization, that is, whether eggs and/or sperm are released or kept inside or on the surface of the parent's body. Although the evolutionary consequences of fertilization mode are far-reaching, transitions in the fertilization mode itself have largely escaped theoretical attention. H...

Projects

Project (1)
Project
Cuckoldry and alloparental care are widespread among animals, but their effects on the fitness of the involved parties are unclear in many instances. The question remains why males of so many species lack effective defenses against cuckoldry. I will empirically examine factors that can mitigate the fitness consequences of being cuckolded and thus contribute to our understanding of what superficially appears as maladaptive behavior. Previous studies of cuckoldry have assumed high costs to the cuckolded male. Here, I include a new approach and question whether the costs incurred by high rates of cuckoldry are indeed as high as the number of foreign offspring in a male’s nest would suggest. Possibilities investigated here are: (1) Indirect fitness benefits reduce the costs suffered by cuckoldry, because parenting males are related to cuckolders or to their female mates. (2) Cuckolded males are themselves the cuckolders of other males. (3) Males reduce their paternal investment in response to cuckoldry. The study will be carried out in the cichlid fish Variabilichromis moorii. The breeding behavior of this species combines social monogamy, biparental care, low brood care investment, large brood sizes, and high and variable rates of multiple paternity. This combination differs from the hitherto studied typical avian and piscine breeding systems, and requires novel solutions to the problem of cuckoldry. Importantly, a so far neglected factor - indirect fitness for cuckolded males - is addressed. The study includes extensive field work and sampling at Lake Tanganyika in Zambia to assess paternity, quantify brood care investment and identify the cuckolding males; comprehensive genetic analyses to reconstruct paternity and relatedness; and laboratory experiments to test male responses to manipulations of their share in paternity, and biases in mate preferences and male-male aggression for or against relatives. Within a study quadrat, the positions of all territorials will be mapped and tissue samples for DNA analysis will be taken from adults and broods. Brood care investment will be quantified in nests within the quadrat, and paternity of the caring males will be determined by microsatellite DNA analyses. Microsatellite profiles will also identify the cuckolding males, e.g. if cuckolders are nearby territorials. Test for elevated relatedness between pair members, and between breeding males and their cuckolders, will inform on potential inclusive fitness gains. Tests for spatial aggregations of relatives will demonstrate whether mating and cuckolding among kin – should there be evidence for this – follows from preferences for relatives or from the kin structure in the population. Finally, laboratory experiments will test whether males decrease their brood care efforts in response to a reduction in their paternity, pair preferentially with related females and bias aggression towards unrelated males.