Temporal constraints on reproduction and growth in a seasonal environment

The variety of life forms is one of the most striking phenomena that have stimulated research in evolutionary biology and ecology over recent decades. The crucial role in defining the most characteristic features of living organisms is dedicated to so-called life history traits (Stearns 1992, Roff 2002). Biological species are characterized by several life history traits such as lifespan, rate of ageing, sexual size dimorphism, but also traits investigated in this work: body size, growth rate, mode of reproduction, and timing and synchrony of breeding. Those traits define functional features of species with consequences going far beyond simple classification. From individual to the ecosystem level, life history traits affect physiology, behaviour but also interactions between species (Davies et al. 2012). Hence, the knowledge about how life history traits evolve is central for understanding important scientific questions but also practical ecological or conservation issues (Allen 2006, Jørgensen et al. 2007, Heino et al. 2015). The great meaning and the potential of our understanding of the sources of evolution of life history traits for understanding ecosystem functioning is the main motivation of my research presented in this thesis. In my thesis I combine theoretical models and empirical work. I aimed at testing hypotheses on the evolution of life history traits in the context of one of the key life history compromises: the evolutionary trade-off between current and future reproduction (Williams 1966). My work was inspired by life histories of species living at a high-latitude Arctic ecosystem of Svalbard archipelago. The empirical part of my thesis, performed to test the predictions of my theoretical research, was conducted in Svalbard in years 2015 2020. The research questions regarding the evolution of body size, growth rate, mode of reproduction and, timing and synchrony of breeding presented in this thesis are oriented around the two subjects described below: the life history trade-off between current and future reproduction under temporal constraints generally and in a high latitude Arctic ecosystem particularly.Doktorgradsavhandlin

Nesting synchrony and clutch size in migratory birds: Capital versus income breeding determines responses to variable spring onset

Synchronous reproduction of birds has often been explained by benefits from nesting together, but this concept fails to explain observed intraspecific variation and climate-mediated changes of breeding synchrony. Here, we present a theoretical model of birds that store resources for reproduction (capital breeders) to show how breeding synchrony, clutch size, and offspring recruitment respond to changes in timing of first possible breeding date. Our approach is based on individual fitness maximization when both prebreeding foraging and offspring development are time constrained. The model predicts less synchronous breeding, smaller clutch size, and higher chances for offspring recruitment in capital breeding birds that advance their nesting. For contrast, we also show that birds that need to acquire resources during egg laying (income breeders) do not change nesting synchrony but increase clutch size along with earlier breeding. The prediction of stronger nesting synchronization of capital breeders in years with late nesting onset is confirmed by empirical data on breeding synchrony of a high-latitude capital breeding sea duck, the common eider (Somateria mollissima). We predict that in warming high-latitude ecosystems, bird species that depend on stored reserves for reproduction are expected to desynchronize their nesting.publishedVersio

Food resource uncertainty shapes the fitness consequences of early spring onset in capital and income breeding migratory birds

Due to climate change, the timing of spring arrival and nesting onset in many migratory bird species have advanced. Earlier spring onsets prolong the available breeding period but can also deteriorate local conditions, leading to increased temporal variation in resource availability. This interaction between phenological shifts in nesting onset and short-term temporal variation in food gain has unknown consequences for fitness of migratory bird species. We model two contrasting breeding strategies to investigate the fitness consequences of stochastically fluctuating food gain and storing of energetic reserves for reproduction. The model was inspired by the biology of common eiders (Somateria mollissima), which store extensive reserves prior to egg laying and incubation (capital breeding strategy), and king eiders (S. spectabilis), which continue to forage during nesting (income breeding strategy). For capital breeders, foraging prior to breeding increases energy reserves and clutch size, but for both strategies, postponing nesting reduces the chances of recruitment. We found that in scenarios with early spring onset, the average number of recruits produced by capital breeders was higher under conditions of stochastic rather than deterministic food gain. This is because under highly variable daily food gain, individuals successful in obtaining food can produce large clutches early in the season. However, income breeders do not build up reserve buffers; consequently, their fitness is always reduced, when food availability fluctuates. For both modeled strategies, resource uncertainty had only a minor effect on the timing of nesting onset. Our work shows that the fitness consequences of global changes in breeding season onset depend on the level of uncertainty in food intake and the degree to which reserves are used to fuel the reproductive effort. We predict that among migratory bird species producing one clutch per year, capital breeders are more resilient to climate-induced changes in spring phenology than income breeders.publishedVersio

Temporal constraints on reproduction and growth in a seasonal environment

The variety of life forms is one of the most striking phenomena that have stimulated research in evolutionary biology and ecology over recent decades. The crucial role in defining the most characteristic features of living organisms is dedicated to so-called life history traits (Stearns 1992, Roff 2002). Biological species are characterized by several life history traits such as lifespan, rate of ageing, sexual size dimorphism, but also traits investigated in this work: body size, growth rate, mode of reproduction, and timing and synchrony of breeding. Those traits define functional features of species with consequences going far beyond simple classification. From individual to the ecosystem level, life history traits affect physiology, behaviour but also interactions between species (Davies et al. 2012). Hence, the knowledge about how life history traits evolve is central for understanding important scientific questions but also practical ecological or conservation issues (Allen 2006, Jørgensen et al. 2007, Heino et al. 2015). The great meaning and the potential of our understanding of the sources of evolution of life history traits for understanding ecosystem functioning is the main motivation of my research presented in this thesis. In my thesis I combine theoretical models and empirical work. I aimed at testing hypotheses on the evolution of life history traits in the context of one of the key life history compromises: the evolutionary trade-off between current and future reproduction (Williams 1966). My work was inspired by life histories of species living at a high-latitude Arctic ecosystem of Svalbard archipelago. The empirical part of my thesis, performed to test the predictions of my theoretical research, was conducted in Svalbard in years 2015 2020. The research questions regarding the evolution of body size, growth rate, mode of reproduction and, timing and synchrony of breeding presented in this thesis are oriented around the two subjects described below: the life history trade-off between current and future reproduction under temporal constraints generally and in a high latitude Arctic ecosystem particularly

Probing of mortality rate by staying alive: The growth-reproduction trade-off in a spatially heterogeneous environment

1. In many annual plants, mollusks, crustaceans and ectothermic vertebrates, growth accompanies reproduction. The growth curves of these organisms often exhibit a complex shape, with episodic cessations or accelerations of growth occurring long after maturation. The mixed allocation to growth and reproduction has poorly understood adaptive consequences, and the life‐history theory does not explain if complex growth in short‐lived organisms can be adaptive. 2. We model the trade‐off between growth and reproduction in a short‐lived organism evolving in a metapopulation. Individuals occupy risky or safe sites throughout their lives, but are uncertain regarding the risk of death. Modelled organisms are allowed to grow and produce offspring at specified time points (moults), although we also consider scenarios that approximate continuous growth and reproduction. 3. Certain combinations of risky to safe sites select for strategies with mixed allocation to growth and reproduction that bet‐hedge offspring production in safe and risky sites. Our model shows that spatially heterogeneous environments select for mixed allocation only if safe sites do not become the prevailing source of recruits, for example, when risky sites are frequent. In certain conditions, growth curves are multi‐phasic, with allocation to growth that stops, remains constant or accelerates during adult life. The resulting complex growth curves are more likely to evolve in short‐lived organisms that moult several times per adult life. 4. Our work shows that spatial heterogeneity can select for growth that accompanies reproduction and provides insights into the adaptive significance of complex growth curves. Short‐lived crustaceans are particularly predisposed to exhibit complex growth patterns as an adaptive response to spatially heterogeneous environments. Our results suggest that standard statistical growth models assuming adult growth rate to only decelerate over life are not well suited to approximate growth curves of short‐lived crustaceans

Should the optimism regarding probability of survival increase during life? Optimal energy allocation in heterogeneous environment in Daphnia.

Badania empiryczne pokazują, że wiele gatunków organizmów żywych rośnie po osiągnięciu dojrzałości jednocześnie lokując energię w reprodukcję. Wymaga to wyjaśnienia, ponieważ istniejące modele historii życia w większości przypadków przewidują zakończenie wzrostu w momencie dojrzewania jeśli środowisko jest bezsezonowe lub cykl życiowy jest nie dłuższy niż jeden sezon. Wpływ heterogeniczności środowiska na ewolucję organizmów od wielu lat pozostaje tematem badań biologii ewolucyjnej, jednak nie był dotąd rozpatrywany w modelach dotyczących wzrostu po dojrzewaniu. W przedstawionym symulacyjnym modelu ewolucji rozpatruję środowisko heterogeniczne pod względem prawdopodobieństwa przeżycia, przy czym organizm nie wie, w jak ryzykownym miejscu się znajduje. W takim przypadku działa mechanizm promujący wzrost optymizmu dotyczącego szans przeżycia – pozostawanie przy życiu staje się wskazówką informującą o niskim poziomie ryzyka w środowisku, co powoduje, że optymalne jest kontynuowanie wzrostu po osiągnięciu dojrzałości. W modelu oprócz strategii o całkowitym przełączeniu ze wzrostu na rozmnażanie, otrzymałam dwa inne typy strategii, w których mieszana alokacja jest elementem utrzymywanym przez dobór naturalny. Jedną z tych strategii jest występowanie okresu czystego wzrostu, następnie wzrostu połączonego z rozmnażaniem, a jeszcze później lokowania wszystkich zasobów w rozród. Druga strategia jest zaskakująca: po okresie rozmnażania następuje ponownie faza wzrostu.Empirical studies show that many organisms grow after maturity and allocate energy to reproduction at the same time. This issue calls for explanation, since the most of previous models of life history evolution predict termination of growth when reproduction starts and environment is either aseasonal or life cycle is no longer than one season. The heterogeneity of environment is one of main research subjects in evolutionary biology, however it has been never studied in theoretical models concerning growth after maturity. In presented simulation model of biological evolution I considered heterogeneous environment with respect to probability of survival, and under assumption that an organism does not know how risky the place is. In such a case natural selection promotes the increase in optimism regarding survival: the fact of being alive can be used as a cue of lower mortality rate in environment, which causes the optimality of growing after reaching maturity. In the model’s results, apart from the strategy of energy allocation with complete switch between growth and reproduction, I received two other types of strategies with mixed allocation maintained by natural selection. In the first type pure growth is followed by the period of mixed allocation with further allocation of all of resources for reproduction. The second type is even more surprising: the phase of growth appears again after a period of pure allocation to reproduction