Reproductive rates under competition

Natuurlijke selectie bevoordeelt individuen die zich zo gedragen dat de genetische bijdrage aan toekomstige generaties maximaal is (maximale fitness). Welke selectieve krachten individueel gedrag vormen en op welke ruimtelijke schaal dat gebeurt, is van cruciaal belang om variatie in gedrag te begrijpen. Daarom is het nodig het effect van natuurlijke selectie op individueel gedrag zoals voortplantingsgedrag te bestuderen. Veel onderzoek heeft zich gericht op het begrijpen van variatie in voortplantingsgedrag. Het blijkt dat naast omgevingsfactoren zoals voedselbeschikbaarheid en nestgelegenheid en de daaruit voortvloeiende effecten op conditie en gezondheid ook de sociale omgeving van een individu het gedrag sterk kan beïnvloeden. Maar hoe dat werkt is vaak niet duidelijk. Zo zijn er bijvoorbeeld tegengestelde effecten van de dichtheid van soortgenoten op het vestigingsgedrag van jonge dieren mogelijk. Enerzijds voorspelt een hoge populatiedichtheid veel competitie en kan zij een negatief effect op de vestiging hebben maar anderzijds kan diezelfde populatiedichtheid samenhangen met een hoge kwaliteit van het leefgebied en dus een positief effect op de vestiging hebben. Niet willekeurige verdeling van individuen over de omgeving creërt zelf ook weer variatie in de lokale sociale omgeving en daarmee variatie in de lokale competitie om hulpbronnen zoals territoria, voedsel en partners. In dit proefschrift bestudeer ik het effect van de sociale omgeving op het broedsucces van Koolmezen (Parus major). Mijn primaire interesse is om de fitness consequenties van legselgrootte onder verschillende sociale omstandigheden te kwantificeren. Dit om na te gaan of sociale omstandigheden selectie op legselgrootte beïnvloeden en daarmee variatie in legselgrootte kunnen verklaren. We creëerden terreinen met verschillende dichtheden en geslachtsverhoudingen van uitgevlogen jongen. Vervolgens hebben we gemeten hoe dit de dispersie en de overleving van de ouders en de groei, dispersie, vestiging en overleving van de jongen beïnvloedde. Onze proefopzet maakte het mogelijk om te onderzoeken of en op welke schaal de sociale omgeving de selectie op legselgrootte beïnvloedde. In de komende samenvatting bespreek ik de proefopzet, daarna geef ik mijn voorspellingen aan de hand van de bestaande theorie en ten slotte bespreek ik de belangrijkste resultaten. ... Zie: Samenvatting.

Eco-evolutionary consequences of dispersal syndromes during colonization in a passerine bird

In most animal species, dispersing individuals possess phenotypic attributes that mitigate the costs of colonization and/or increase settlement success in new areas (‘dispersal syndromes’). This phenotypic integration likely affects population dynamics and the direction of selection, but data are lacking for natural populations. Using an approach that combines population dynamics, quantitative genetics and phenotypic selection analyses, we reveal the existence of dispersal syndromes in a pied flycatcher (Ficedula hypoleuca) population in The Netherlands: immigrants were larger, tended to have darker plumage, bred earlier and produced larger clutches than local recruits, and some of these traits were genetically correlated. Over time, the phenotypic profile of the population gradually changed: each generation advanced arrival and breeding and exhibited longer wings as the result of direct and indirect selection on these correlated traits. Although phenotypic attributes of immigrants were favored by selection during the early phase of colonization, observed phenotypic changes were similar for immigrants and local recruits. We propose that immigrants facilitated initial population establishment but that temporal changes likely resulted from climate change-induced large scale selection. This study highlights that newly established populations are of non-random composition and that phenotypic architecture affects evolutionary population trajectories

Eco-evo-devo of migration syndromes

Many species exhibit partial migration: only a subset of the population migrates, while the rest stays at home. Understanding partial migration is important, since it effects the population dynamics, niche breadth, gene flow, and reproductive isolation. For this, it is important to realize that migrants are not a random sample of the population but differ systematically from residents in a whole suite of traits. We combine field studies, mesocosm experiments, and individual-based simulations to unravel this ’migration syndrome’ in partially migrating populations of three-spined sticklebacks in the Netherlands

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

State dependence explains individual variation in nest defence behaviour in a long-lived bird

Parental care, such as nest or offspring defence, is crucial for offspring survival in many species. Yet, despite its obvious fitness benefits, the level of defence can consistently vary between individuals of the same species. One prominent adaptive explanation for consistent individual differences in behaviours involves state dependency: relatively stable differences in individual state should lead to the emergence of repeatable behavioural variation whereas changes in state should lead to a readjustment of behaviour. Therefore, empirical testing of adaptive state dependence requires longitudinal data where behaviour and state of individuals of the same population are repeatedly measured. Here, we test if variation in states predicts nest defence behaviour (a 'risky' behaviour) in a long-lived species, the barnacle goose Branta leucopsis. Adaptive models have predicted that an individual's residual reproductive value or 'asset' is an important state variable underlying variation in risk-taking behaviour. Hence, we investigate how nest defence varies as a function of time of the season and individual age, two state variables that can vary between and within individuals and determine asset. Repeated measures of nest defence towards a human intruder (flight initiation distance or FID) of females of known age were collected during 15 breeding seasons. Increasing values of FID represent increasing shyness. We found that females strongly and consistently differed in FID within- and between-years. As predicted by theory, females adjusted their behaviour to state by decreasing their FID with season and age. Decomposing these population patterns into within- and between-individual effects showed that the state-dependent change in FID was driven by individual plasticity in FID and that bolder females were more plastic than shyer females. This study shows that nest defence behaviour differs consistently among individuals and is adjusted to individual state in a direction predicted by adaptive personality theory