Jonathan Henshaw

• PhD
• Professor (Assistant) at University of Freiburg

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...

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...

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...

The aesthetic preferences of potential mates have driven the evolution of a baffling diversity of elaborate ornaments. Which fitness benefit—if any—choosers gain from expressing such preferences is controversial, however. Here, we simulate the evolution of preferences for multiple ornament types (e.g., “Fisherian,” “handicap,” and “indicator” ornam...

Artificial gene drives offer a promising approach for controlling populations of agricultural pests, invasive species and disease vectors, such as malaria-carrying mosquitoes. Gene-drive alleles induce a transmission bias, meaning there is a greater than 50% probability that they will be inherited by offspring, facilitating their rapid propagation...

Phenotypic traits rarely evolve in isolation. Instead, multiple traits typically interact, resulting in complex coevolutionary dynamics. Such dynamics can be predicted using mathematical frameworks such as adaptive dynamics and quantitative genetics. Selection gradients play a crucial role in these frameworks, describing the direction and strength...

Why do animals display sexual ornaments – to attract mates, to compete for access to them, or both? In the broad-nosed pipefish (Syngnathus typhle), ornamented females commonly compete for access to males, whereas choosy males provide uniparental care. During courtship, females show a dynamic ornament, consisting of a row of dark B-shaped signs alo...

In the 1980s, groundbreaking theoretical studies showed that orna- ments displayed during courtship can coevolve with preferences for such ornaments, leading to extreme exaggeration of both traits. Later mod- els cast doubt on such ‘runaway’ sexual selection, showing that even a small cost of preferences can prevent exaggerated ornaments from per-...

A long-standing problem in evolutionary theory is to clarify in what sense (if any) natural selection cumulatively improves the design of organisms. Various concepts, such as fitness and inclusive fitness, have been proposed to resolve this problem. In addition, there have been attempts to replace the original problem with more tractable questions...

Competition over resources is often decided via aggressive interactions, which may or may not escalate to all-out fights. Weapons and body size play important roles in such interactions, as they often provide reliable cues of an individual’s fighting ability. In contrast, traits like nonfunctional display “weapons” may dishonestly exaggerate fighti...

An individual's optimal investment in parental care potentially depends on many variables, including its future fitness prospects, the expected costs of providing care and its partner's expected or observed parental behaviour. Previous models suggested that low-quality parents could evolve to exploit their high-quality partners by reducing care, le...

Anisogamy—the size dimorphism of gametes—is the defining difference between the male and female sexual strategies. Game-theoretic thinking led to the first convincing explanation for the evolutionary origins of anisogamy in the 1970s. Since then, formal game-theoretic models have continued to refine our understanding of when and why anisogamy shoul...

Exaggerated ornaments often evolve due to the mating preferences of the opposite sex. Genetic correlations between preferences and ornaments can lead both traits to elaborate dramatically in tandem, in a process known as ‘Fisherian runaway’. However, in most previous models of Fisherian runaway, elaborate ornaments are not expected to persist when...

Unlabelled: Mating patterns in animal populations can respond to environmental conditions and consequently vary across time. To examine this variation in nature, studies must include temporal replicates from the same population. Here, we report temporal variation in genetic parentage in the socially monogamous cichlid Variabilichromis moorii from...

Why do males typically compete more intensely for mating opportunities than do females and how does this relate to sex differences in gamete size? A new study provides a formal evolutionary link between gamete size dimorphism and ‘Bateman gradients’, which describe how much individuals of each sex benefit from additional matings.

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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 ;...

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...

Significance How does sexual selection differ between males and females? What is its role in the speciation process? Answering such questions requires a reliable method to measure sexual selection, so that we can compare its strength between the sexes and across taxa. The development of appropriate measures has led to sustained controversy, however...

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...

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...

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...

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...