Seasonality of reproduction in Bathyergidae is a function of group size: A novel hypothesis (Rodentia)

Abstract

In the African mole-rat family (Bathyergidae), species show both year-round and seasonal breeding patterns even though all species inhabit regions with varying seasonal rainfall patterns (a well-known selection driver of seasonal breeding). This short review suggests a novel hypothesis explaining why some African mole-rat species breed seasonally and others year-round. Namely, group-living African mole-rat species (with a mean colony size greater than five) exhibit an aseasonal reproduction pattern, as breeders, particularly females, possess year-round high body conditions. This is likely due to access to abundant and high-quality resources (food and water) throughout the year and reduced frequency of engaging in strenuous activities, such as digging, due to the increased efficiency of locating and retrieval of resource as a function of group size. While in the solitary and social species, with mean colony sizes of five or less, there are too few colony members to provide sufficient cooperative care benefits, the breeders show a seasonality to their body condition and thus breeding investment. As such, we hope to start a discussion on how group size could affect circannual breeding rhythms and propose some avenues for future research.

A comparison of the population ecology of 4 Cryptomys hottentotus subspecies

“…However, differing recruitment rates (differing litter size, and offspring survival rates) between subspecies are likely the result of the differing colony size of subspecies and not the other way around (Houslay et al 2020). Hart and Bennett (2023) have recently hypothesized that mole-rat species with larger colony sizes (as seen in the Mahali and Natal mole-rat) exhibit an aseasonal pattern of reproduction and increased litter size and pup survival because breeders, particularly females, possess year-round high body conditions, likely due to access to abundant and high-quality resources (food and water) throughout the year due to increased efficiency of locating and retrieval of resource as a function of colony size. Alternatively, in social species with smaller colony sizes-such as the highveld mole-rat and, to some extent, the common mole-rat, have fewer colony members to provide sufficient cooperative care benefits, breeders show a seasonality to their body condition and thus breeding investment and litter sizes (Hart and Bennett 2023).…”

“…To better understand underlying proximate (ecological) and ultimate (evolutionary) factors behind these adaptations, research often focuses on particular orders, families, or species and particular adaptations. One such area of focus is variation in social organization—specifically colony structure or size (Ebensperger and Cofré 2001; Clutton-Brock 2021) and body mass (Blackburn and Gaston 1994, 1998; Hantak et al 2021) in rodents—and in particular, African mole-rats in the Family Bathyergidae (Faulkes et al 1997; Faulkes and Bennett 2013; Hart and Bennett 2023). African mole-rats are subterranean rodents endemic to sub-Saharan Africa occurring in underground burrows and demonstrate broad variability in social organization and morphologies, especially body mass (Bennett and Faulkes 2000).…”

The best of both worlds: no apparent trade-off between immunity and reproduction in two group-living African mole-rat species

“…Mammals may form groups ranging from small pair-bonded units to large organized groups with highly complex social interactions that have been compared to those of eusocial insects, such as bees, ants and termites [2][3][4]. Compared with the so-called solitary mammalian species, which only come together to breed or when females have young, group-living or social mammalian species have a number of benefits that increase the individual fitness of group members, including, but not limited to, enhanced protection against predators, increased energy and water savings (through increased foraging efficiency and resource accessibility), access to potential mates, access to social information, and possibly the benefit of alloparental care (offspring receive care not only from their parents but also from other group members) [2,5,6]. However, individuals of a species that partake in a group-living strategy also face several consequences that are likely not experienced by their solitary-living counterparts; these include increased risk of exposure to diseases and parasites through intra-group transmission, and intraspecific competition for both resources and the opportunity to reproduce [7][8][9].…”