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Within species support for the expensive tissue hypothesis: a negative association between brain size and visceral fat storage in females of Pacific seaweed pipefish
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.ORCID iD: 0000-0002-0144-2893
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The brain is one of the most energetically expensive organs in the vertebrate body. Consequently, the high cost of brain development and maintenance is predicted to constrain adaptive brain size evolution (the expensive tissue hypothesis, ETH). Here, we test the ETH in a teleost fish with predominant female mating competition (reversed sex-roles) and male pregnancy, the pacific seaweed pipefish Syngnathus schlegeli. The relative size of the brain and other energetically expensive organs (kidney, liver, heart, gut, visceral fat, ovary/testis) was compared among three groups: pregnant males, non-pregnant males and egg producing females. Brood size in pregnant males was unrelated to brain size or the size of any other organ, whereas positive relationships were found between ovary size, kidney size and liver size in females. Moreover, we found that the size a suite of energetically expensive organs (brain, heart, gut, kidney, liver) as well as the amount of visceral fat did not differ between pregnant and non-pregnant males. However, we found marked differences in relative size of the expensive organs between sexes. Females had larger liver and kidney than males, whereas males stored more visceral fat than females. Furthermore, in females we found a negative correlation between brain size and the amount of visceral fat, whereas in males a positive trend between brain size and both liver and heart size was found. These results suggest that, while the majority of variation in the size of various expensive organs in this species likely reflects that individuals in good condition can afford to allocate resources to several organs, the cost of the expensive brain was visible in the visceral fat content of females, possibly due to the high costs associated with female egg production. 

Keyword [en]
The expensive tissue hypothesis, Brain size evolution, pipefish
National Category
Evolutionary Biology
URN: urn:nbn:se:uu:diva-262071OAI: oai:DiVA.org:uu-262071DiVA: diva2:852170
Available from: 2015-09-08 Created: 2015-09-08 Last updated: 2015-10-12
In thesis
1. Thinking in water: Brain size evolution in Cichlidae and Syngnathidae
Open this publication in new window or tab >>Thinking in water: Brain size evolution in Cichlidae and Syngnathidae
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Brain size varies greatly among vertebrates. It has been proposed that the diversity of brain size is produced and maintained through a balance of adaptations to different types and levels of cognitive ability and constraints for adaptive evolution. Phylogenetic comparative studies have made major contributions to our understanding of brain size evolution. However, previous studies have nearly exclusively focused on mammalian and avian taxa and almost no attempts have been made to investigate brain size evolution in ectothermic vertebrates.

In my thesis, I studied brain size evolution in two groups of fish with extreme diversity in ecology, morphology and life history, Cichlidae and Syngnathidae. Using phylogenetic comparative methods, I investigated four key questions in vertebrate brain size evolution; cognitive adaptation, sexual selection, phenotypic integration and energetic constraints.

I have demonstrated i) that phenotypic integration can link functionally unrelated traits, and this may constrain independent evolution of each part involved or promote concerted evolution of an integrated whole, ii) that brain-body static allometry constrains the direction of brain size evolution, even though the static-allometry showed ability to evolve, allowing evolution of relative brain size under allometric constraints, iii) that the energetic constraints of development and maintenance of brain tissue is an important factor in forming the diversity in brain size in cichlids and syngnathids, both at macroevolutionary and microevolutionary time scales, and iv) that adaptation for feeding and female mating competition may have played key roles in the adaptive evolution of brain size in pipefishes and seahorses. To conclude, my thesis shows the strong benefit of using fish as a model system to study brain size evolution with a phylogenetic comparative framework.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 50 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1286
brain evolution, phylogenetic comparative method, the expensive tissue hypothesis, cichlid, pipefish, seahorse
National Category
Evolutionary Biology
Research subject
Biology with specialization in Animal Ecology
urn:nbn:se:uu:diva-262216 (URN)978-91-554-9333-2 (ISBN)
Public defence
2015-10-29, Zootissalen, Villavägen 9, tr.2, Uppsala, 10:15 (English)
Available from: 2015-10-07 Created: 2015-09-10 Last updated: 2015-10-12

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