Abstract
One of the major mechanisms responsible for the animals’ fitness dynamics is fecundity. Fecundity as a trait does not evolve independently, and rather interacts with other traits such as body and egg size. Here, our aim was to correctly infer the macroevolutionary trade-offs between body length, egg length, and potential fecundity, using cephalopods as study model. The correlated evolution among those traits was inferred by comparative phylogenetic methods. Literature data on biological and reproductive traits (body length, egg length, and potential fecundity) was obtained for 90 cephalopod species, and comparative phylogenetic methods based on a previous molecular phylogeny were used to test the correlated evolution hypothesis. Additionally, we estimated the phylogenetic signal and fitted five different evolutionary models to each trait. All traits showed high phylogenetic signal, and the selected model suggested an evolutionary trend toward increasing body length, egg length, and fecundity in relation to the ancestral state. Evidence of correlated evolution between body length and fecundity was observed, although this relationship was not detected between body length and egg length. The robust inverse relationship between fecundity and egg length indicates that cephalopods evolved a directional selection that favored an increase of fecundity and a reduction of egg length in larger species, or an increase in egg length with the concomitant reduction of fecundity and body length in order to benefit offspring survival. The use of phylogenetic comparative methods allowed us to properly detect macroevolutionary trade-offs.
Highlights
Life history traits of marine organisms are important for ecological and evolutionary studies as components of Darwinian fitness, but are of crucial relevance in fisheries and aquaculture
This approach has been scarcely used in comparative studies of cephalopods, and the assessment of phylogenetic signal has only been conducted in five publications (i.e., Ibáñez et al, 2018, 2019, 2021; Anderson and Marian, 2020; Ponte et al, 2021)
Our research is among the few studies correctly addressing trait comparisons for cephalopods, suggesting that further research should incorporate this approach in comparative biology of cephalopods
Summary
Life history traits of marine organisms are important for ecological and evolutionary studies as components of Darwinian fitness, but are of crucial relevance in fisheries and aquaculture. There are multiple examples of micro- and macroevolutionary trade-offs (e.g., Stearns, 1992; Badyaev, 2002; Roff, 2002; Arendt, 2003; Poulin and Mouillot, 2004) including for instance, phenotypic correlations between offspring size and fecundity or survival, and between body size and longevity, their interpretation has been controversial This is due to uncertainties in determining whether the increase of performance in one trait causes a decrease of performance in another trait, or if traits interact functionally (Zera and Harshman, 2001). A trade-off in life history traits could be the result of an evolutionary trend caused by clades evolving separately, as was detected in mammals, where different groups display convergent evolution in body size and active trends of size at maturity and longevity (Lartillot and Delsuc, 2012)
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