Intraspecific variation in phenotypic plasticity

Kaisa Susanna Välimäki

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Understanding the causes and consequences of phenotypic divergence among natural populations is one of the fundamental goals of evolutionary biology. Phenotypic differentiation among populations can arise through divergent selection leading to local adaptation, phenotypic plasticity, or a combination thereof. Selection can also influence the expression of plasticity in different environments resulting in divergence in phenotypic plasticity. It is therefore essential to know how plasticity evolves under divergent ecological conditions when aiming to understand the mechanisms that underlie phenotypic differentiation.

In this thesis I have explored the extent of variation in phenotypic plasticity across a range of locally adapted nine-spined stickleback (Pungitius pungitius) populations from different habitats. Pond and marine populations have diverged in a suite of morphological, life-history and behavioural traits. This divergence has been thought to stem from the absence of piscine predators and interspecific competitors combined with the high intraspecific competition in pond habitats. My aims were to establish if and how predator cues and variation in resource levels induce phenotypic plasticity in the nine-spined stickleback, and whether phenotypic plasticity has also diverged as a response to divergent selective pressures in different environments and between sexes. I quantified phenotypic plasticity in a set of traits that form a continuum from very labile to developmentally fixed ones.

The results show that plasticity was induced by both predator presence and food availability. Fish responded to perceived predation risk with reduced growth rates, decreased body condition and by behavioural changes. Food restriction resulted in slower growth and reduced investment in energy storage, but increased feeding activity and risk-taking. The results were largely in accordance with my predictions of increasing plasticity from morphology through life history traits to behaviour. The results also show that population divergence in phenotypic plasticity is habitat dependent. Pond populations responded more strongly to food treatment in terms of behaviour and growth, while marine fish exhibited stronger responses to predation treatment. However, in the case of brain size and lateral line system, predation-induced plastic responses were detected only in pond fish that had evolved in the absence of piscine predation. I also detected strong sexual dimorphism in both trait means and phenotypic plasticity, uncovering a very important determinant of within population variation in phenotypic plasticity.

Taken together, the results of my thesis demonstrate how natural and sexual selection do not only affect phenotypic traits themselves, but also the plasticity of the traits. The resultant adaptive variation in phenotypic plasticity is present both between and within populations. In some traits, plasticity was greater whenever the selective pressure was stronger, while in other traits the increased plasticity was coupled with relaxed selection due to the lack of piscine predation in ponds. My thesis demonstrates that the response of phenotypic plasticity to natural selection is context dependent. The results also work to advance our knowledge on the maintenance of phenotypic variation.
Translated title of the contributionIlmiasullisen muuntelun lajinsisäinen vaihtelu
Original languageEnglish
Place of PublicationHelsinki
Print ISBNs978-952-10-8427-0
Electronic ISBNs978-952-10-8428-7
Publication statusPublished - 2012
MoE publication typeG5 Doctoral dissertation (article)

Fields of Science

  • 1181 Ecology, evolutionary biology

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