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Fast life-histories are associated with larger brain size in killifishes
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0002-3705-1907
Stockholm University, Faculty of Science, Department of Zoology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Comparative studies suggest a negative relationship between pace of life-history, and relative energetic investment into brain size. However, since brain size typically evolves as a correlated response to selection on body size, any lag in brain size evolution will result in a shift in relative brain size (e.g. small body – large relative brain size).Coevolution between body size and life-history hence has the potential to drive secondary associations between relative brain size and life-history, when body size is correlated with life history. However, as far as we know, the relationship between relative brain size and life-history strategy has not been examined in systems that simultaneously present marked contrasts in life-history but no concordant shifts in body size. Using a common garden approach, we test the association between relative brain size and life-history in 21 species of killifish; a study system that fulfils the aforementioned requirements. Contrary to the prediction that brain size evolves through energetic trade-offs with life-history, we found that adults, but not juveniles, of fast-living species had larger relative brain sizes. Rather than an energetic link to life-history, our results suggest that fast- and slow-living species differ in terms of how cognitively demanding environments they inhabit are, or alternatively in the ontogenetic timing of somatic vs. neural growth.

Keywords [en]
Expensive Brain Hypothesis, Energy trade-off Hypothesis, comparative analysis, life-history strategies, trade-offs, relative brain size
National Category
Evolutionary Biology
Research subject
Ethology
Identifiers
URN: urn:nbn:se:su:diva-169673OAI: oai:DiVA.org:su-169673DiVA, id: diva2:1324089
Available from: 2019-06-13 Created: 2019-06-13 Last updated: 2019-06-13Bibliographically approved
In thesis
1. Behavioural, physiological and morphological correlates of life-history in killifishes − a macroevolutionary approach
Open this publication in new window or tab >>Behavioural, physiological and morphological correlates of life-history in killifishes − a macroevolutionary approach
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Life-histories commonly evolve along a continuum from short-lived and fecund, to long-lived and less fecund. Because life-history traits are mostly components of reproduction and survival, understanding the causes and consequences of life-history variation is at the core of evolutionary biology. This thesis aims to identify what other key traits (e.g. behavioural, physiological and morphological traits) covary with life-history, and why. Numerous hypotheses describe how life-history might be associated with other traits, with life-history trade-offs often considered to be a primary driver of any such relationships. For example, since resources are limited, increased investment in one trait must lead to decreased investment in one or several other traits, all else equal. Hypotheses on the relationship between life-history and other traits have been tested in many studies, but empirical studies in controlled experimental settings are rare. In this thesis I explore how behaviour, physiology and morphology relate to variation along the life-history continuum from fast to slow, in a system with substantial variation in life-history traits - the killifishes.

I began by exploring the patterns of egg to body size allometry in killifishes (Paper I), where species with faster life-histories showed indications of constraints on the independent evolution of egg size and body size. Furthermore, I found evidence of differences in variance and in the rates of evolution of egg size and body size across species, potentially caused by the colonisation of ephemeral habitats, which could have selected for adaptations that lead to differences in size.

I then performed a comparative common garden study (Paper II) of the pace-of-life syndrome hypothesis, which predicts that species with fast life-histories should take larger risks in order to maintain their increased reproductive rate. I obtained data on risk taking behaviours, including movement, tendency to enter an open environment, and aggressiveness, in addition to metabolic rate, for 20 species of killifish, with multiple replicates per species. The results indicated trait dependent associations with life-history, where aggression seemed to correlate positively with speed of life-history, in congruence with our prediction.

Next, my colleagues and I assessed the association between life-history and sexual selection (Paper III), in order to determine if investment in secondary sexual traits might be traded off against survival in killifish. Fin size was found to be negatively associated with escape performance in a simulated predator attack, suggesting survival costs for individuals with large fins. Importantly, fin size was also positively associated with the speed of life-history, supporting the hypothesis that costs to survival probability is lower in fast-living species.

Lastly, I tested the hypothesized negative covariation between relative brain size and speed of life-history, by collecting and analysing brain size measurements for 21 species of killifish (Paper IV). Surprisingly, a positive relationship between speed of life-history and relative brain size was found for adults, although juveniles did not differ in relative brain size. This implies at least one of two things: either there is no need to trade off brain size with life-history since resource acquisition is higher, or brain size and life-history are traded-off with other traits.

In conclusion, I show that previously found trade-offs between life-history and investment in other costly traits are only sometimes present, when tested in a system with substantial divergences in the speed of life-history. I also provide evidence for a trait dependent association between life-history and among species differences in risk-taking and metabolic rate.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2019. p. 19
Keywords
brain size evolution, comparative analysis, life-history continuum, risk-taking behaviour, sexual selection, trade-offs
National Category
Behavioral Sciences Biology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-169666 (URN)978-91-7797-759-9 (ISBN)978-91-7797-760-5 (ISBN)
Public defence
2019-09-06, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. 4: Manuscript.

Available from: 2019-08-14 Created: 2019-06-13 Last updated: 2019-08-19Bibliographically approved

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