Ecological and behavioural drivers of offspring size in marine teleost fishes

Abstract

Aim: Our aim was to evaluate the role of ecological and life-history factors in shaping global variation in offspring size in a marine clade with a diverse range of parental care behaviours. Location: Global. Time period: Data sourced from literature published from 1953 until 2019.Major taxa studied: Marine teleost fishes. Methods:We compiled a species-level dataset of egg and hatch size for 1,639 species of marine fish across 45 orders. We used Bayesian phylogenetic mixed models to evaluate the relationship between offspring size and environmental factors (i.e., mean temperature, chlorophyll-a and dissolved oxygen content together with their annual variation), as well as latitude, reproductive strategy, parental body size and fecundity. We also tested long-standing hypotheses about the co-evolution of offspring size and the presence of parental care in BayesTraiTs. Results:After controlling for parental body size and phylogenetic history, we find that increased egg size is associated with colder and oxygen-rich waters, while hatch size further depends on food supply and the reproductive strategy exhibited by the species. Irrespective of the initial investment in egg size, species with parental care or demersal egg development yield larger hatchlings compared to pelagic spawners.We also demonstrate that hatch size has co-evolved with advanced forms of care in association with parental body but fail to find a relationship with other types of care. Main conclusions:Our study shows that parental care behaviours, together with environmental context, influence the evolution of classic life-history trade-offs on a global scale. While the initial investment in eggs is driven primarily by temperature and oxygen content, hatch size also reflects the impact of care an offspring has received throughout development. In support of the 'offspring-first' hypothesis, we find that an increase in hatch size drives the evolution of advanced care provision.

Terrestrial reproduction and parental care drive rapid evolution in the trade-off between offspring size and number across amphibians

“…However, producing larger offspring comes at the cost of having fewer of them [ 1 , 2 ], a theoretical prediction repeatedly supported in many animal and plant species and populations [ 5 , 7 , 8 ]. Surprisingly, despite much research, it is still unclear whether and how selective pressures related to environmental conditions and type of parental care drive evolutionary changes in the offspring size–number trade-off [ 9 – 20 ]. Answering this question is fundamental not only for advancing theory, but also because these life history traits influence the demographic trajectory of natural and introduced populations [ 21 – 25 ] and their ability to overcome many anthropogenic stressors [ 24 , 26 – 28 ].…”

“…Subsequently, higher offspring survival should promote additional parental investment, such as in larger eggs [ 13 , 52 , 53 ]. This is because, while larger eggs take longer to hatch and thus require prolonged parental protection, they are of higher fitness value to parents as they result in larger larvae or juveniles that suffer low mortality and reach sexual maturity early [ 20 ].…”

“…Offspring number rather than offspring size may, however, be the target of selection. Environmental conditions can drive brood size evolution [ 19 , 27 ] since they determine the mortality risks on eggs and young, for example, due to predation, desiccation, thermoregulation, or oxygen availability [ 17 , 20 , 54 , 55 ], and the amount of resources available to females for provisioning their eggs and young posthatching/birth in caring species [ 17 ]. Discovering which trait in the trade-off is under selection is thus not trivial because reasons as to why females should invest in larger or in more offspring may differ and a change in one of the traits in the trade-off does not always lead to a proportional change in the other.…”

“…Comparative studies on the relative importance of the drivers of offspring size and number reach different conclusions. For example, some found that eggs are larger in caring than noncaring fish species [ 11 , 13 , 20 ], but egg size is unrelated to parental care in insects [ 9 ] and neonatal size is unrelated to any male care behaviors in mammals [ 56 ]. Likewise, studies in amphibians disagree on whether care, terrestrial egg development, or neither is associated with larger eggs or smaller clutches [ 10 , 12 , 14 – 16 ].…”