Integration of proximate and evolutionary explanation of reproductive strategy: The case of callitrichid primates and implications for human biology

Abstract

We offer examples of how proximate and evolutionary forms of argument may inform each other in better understanding reproductive strategy in callitrichid primates, the smallest of the anthropoid primates. In addition, we illustrate how comparative approaches, when applied judiciously, can aid in the formulation of hypotheses regarding even seemingly unique traits within a taxonomic group. In the first example, examination of the nature of genetics in cytokine systems that leads to altered ovulation number in sheep suggests some relatively simple changes could explain both the adaptation of increased ovulation number in marmosets and the subsequent decrease in ovulation number in the closely related species, callimico. In the second example, the role of body size and phylogeny in explaining the role of maternal energy constraints upon gestation and lactation is explored, leading to additional hypotheses regarding these relations in a species that is both small but also in a phylogenetic line selected for slow reproduction. Finally, the role of comparative data in the study of proximate and evolutionary explanations of "unique" human reproductive strategies is discussed.

Do mothers prefer helpers or smaller litters? Birth sex ratio and litter size adjustment in cotton‐top tamarins (Saguinus oedipus)

“…The majority of callitrichid litters are dizygotic (nonidentical) twins and triplets, but litter sizes of up to six have been recorded in captive Callithrix jacchus (Tardif et al 2013). Although litter size is dictated largely by the number of ova matured and released (Tardif and Ross 2009), single infant births typically result from reabsorption of one or more embryos (in the callitrichids, this is facilitated by delayed embryonic development; females have an extended period of time in which to cease investing in a reproductive attempt if it is no longer profitable to do so; Tardif and Ross 2009). This suggests that primiparous females may reabsorb one or more embryos to reduce their current reproductive burden and optimize their future reproductive success Jaquish 1994, 1997;Jaquish et al 1996).…”

After short interbirth intervals, captive callitrichine monkeys have higher infant mortality

“…To better understand these reproductive processes across primates, we analyzed a large dataset (n = 15,852) of births with known IBIs in nine species of callitrichine monkeys—an American primate clade that routinely produces litters (of fraternal twins and triplets) and relies on cooperative care to raise offspring ( Haig, 1999 ; Tardif, 1996 ; Tardif and Ross, 2009 ). We derived these data from demographic records of zoo and laboratory populations spanning 80 years (1938–2018 ( McCoy et al., 2019 )).…”

Information transfer through food from parents to offspring in wild Javan gibbons

“…Moreover, according to the informational hypothesis, novel or difficult-to-access/process food items are more likely to be transferred, regardless of their nutritional value.Empirical findings in support of the nutritional hypothesis have been mostly found in cooperatively breeding primate species, such as the callitrichids, including tamarins and marmosets 9-11 . In these species, females typically produce 2-3 litters and become pregnant while lactating, which poses a greater energetic burden for the females [12][13][14] . Callitrichid parents actively participate in care-giving and food-provisioning to offspring to facilitate weaning process, and thereby shift their investment (e.g.…”