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Anti-predation traits in marine bivalves along a latitudinal gradient

Stelwagen, Tjibbe (2018) Anti-predation traits in marine bivalves along a latitudinal gradient. Master's Thesis / Essay, Marine Biology.


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From high to low latitudes, species richness tends to increase with striking universality. The mechanism explaining this latitudinal diversity gradient (LDG) remains elusive, but the LDG seems to arise from a complex combination of rates of origination, extinction, and dispersal of organisms. In the underlying evolutionary process, biotic interactions and especially predation pressure, play important roles. The relative importance of these various interactions also follow a latitudinal gradient. Along the gradient, environmental stability and available resources increase equatorward, allowing for an increasingly broad scope of possible ecological adaptations to predation combined with increased selective pressure. This creates increasing potential for evolutionary arms races enabling escalated development of anti-predation traits. In tandem, organisms at higher latitudes are more likely to adapt to abiotic conditions as the biotic environment becomes less rigorous and the abiotic environment more. This raises the question: “Does the expression of anti-predation traits follow the latitudinal richness gradient?” I investigating the marine LDG and using marine bivalves as a model system and shell traits (thickness, length, body mass to shell weight ratio and frequency of occurrence of drilling holes) as indicators for escalation. I found that escalation is not universally occurring at similar latitudes nor are there indications that escalation only occurs around the equator. Escalation is not predicted by the LDG, but is though most likely to occur around the equator and least likely at high latitudes. For escalation to occur highly selective predation pressure in a stable environment with high productivity is supposedly necessary to persist over long time scales. At high latitudes this would be disrupted by cycles of glaciations. I propose that as a result of glacial cycles, escalation occurring at higher latitudes is followed by de-escalation in cold periods. This resets the evolutionary arms race, which carries on around the equator.

Item Type: Thesis (Master's Thesis / Essay)
Supervisor name: Piersma, T.
Degree programme: Marine Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 24 Aug 2018
Last Modified: 10 Sep 2018 12:53

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