Cryptomys Hottentotus Mahali)

Canadian Journal of Zoology Filling in the holes: The reproductive biology of the understudied Mahali mole-rat (Cryptomys hottentotus mahali) Journal: Canadian Journal of Zoology Manuscript ID cjz-2020-0158.R1 Manuscript Type: Article Date Submitted by the 15-Mar-2021 Author: Complete List of Authors: Hart, Daniel; University of Pretoria, Zoology and entomology Medger, Katarina; University of Pretoria Mammal Research Institute, Zoology and Entomology van Jaarsveld,Draft Barry; University of Pretoria Department of Zoology and Entomology, Zoology and Entommology Bennett, Nigel; University of Pretoria Mammal Research Institute Is your manuscript invited for consideration in a Special Not applicable (regular submission) Issue?: REPRODUCTION < Discipline, Reproductive suppression, Cooperative Keyword: breeding, Opportunistic breeder, Aseasonal, Mahali mole-rat, Cryptomys hottentotus mahali © The Author(s) or their Institution(s) Page 1 of 41 Canadian Journal of Zoology 1 Filling in the holes: The reproductive biology of the understudied Mahali mole- 2 rat (Cryptomys hottentotus mahali) 3 D.W. Hart●1, K. Medger2, B. van Jaarsveld1, N.C. Bennett2 4 1Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 5 0028, South Africa 6 2Mammal Research Institute, Department of Zoology and Entomology, University of 7 Pretoria, Private Bag X20, Hatfield 0028, South Africa 8 9 ● Corresponding author 10 D.W. Hart 11 Department of Zoology and Entomology,Draft University of Pretoria South Africa, Pretoria 12 Phone no. +27 84 5744257 13 Email:[email protected] 14 15 16 17 18 19 20 21 22 23 © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 2 of 41 24 Abstract 25 African mole-rats have provided great insight into mammalian evolution of sociality and 26 reproductive strategy. However, some species have not received attention, and these may 27 provide further insights into these evolutionary questions. The cooperatively breeding Mahali 28 mole-rat, Cryptomys hottentotus mahali (Roberts, 1913), is one such species. Body mass, 29 reproductive-tract morphometrics, gonad histology, and plasma reproductive hormone 30 concentrations were studied for breeding and non-breeding males and females over one year. 31 This study aimed to discern if this species exhibits a seasonal or aseasonal breeding pattern 32 and whether there is a relaxation of reproductive suppression at any point in the year in non- 33 breeding animals. The pattern of reproductive relaxation during the wetter months is similar 34 to other African mole-rat species. InterestinglyDraft births and pregnant breeding females were 35 recorded throughout the year, thus indicating an aseasonal breeding strategy, despite 36 inhabiting a region that experience seasonal rainfall. However, there were periods of the year 37 favouring increased reproduction to enable an increased likelihood of offspring survival. This 38 suggests that the Mahali mole-rat may be an opportunistic breeder possibly brought about 39 by the benefits of living in a cooperatively breeding group and potentially moving into more 40 arid environments that were previously unexploited by the genus Cryptomys. 41 Keywords: Reproduction, Opportunistic breeder, Aseasonal, Reproductive suppression, 42 Mahali mole-rat, Cryptomys hottentotus mahali, Cooperative breeding 43 44 45 46 47 © The Author(s) or their Institution(s) Page 3 of 41 Canadian Journal of Zoology 48 Introduction 49 The study of the subterranean family, the Bathyergidae (African mole-rats), has allowed for 50 many essential revelations in mammalian evolution, behaviour and physiology (Bennett and 51 Faulkes 2000; Sherman et al. 2017). Furthermore, this family provides an important study 52 system for the better understanding of how mammals adapt behaviourally, physiologically 53 and molecularly to their inhibiting environment (Broekman et al. 2006; Eigenbrod et al. 2019; 54 Ivy et al. 2019; Logan et al. 2020; McGowan et al. 2020; Barker et al. 2021). 55 56 A focal point of research on African mole-rats includes the broad spectrum of social 57 organisation found in the family Bathyergidae as well as their range of reproductive 58 strategies. Social organisation in AfricanDraft mole-rats ranges from strictly solitary species 59 through to truly social (colony size range: 2-20 in social species) to eusocial (colony size range: 60 2-300 in eusocial species), with breeding occurring either seasonally or aseasonally (breeding 61 throughout the year) depending on the species (Bennett and Faulkes 2000). The aridity food- 62 distribution hypothesis (AFDH), which correlates the sociality of mammals with habitat 63 aridity, is the primary hypothesis used to explain the phenomena of differing degrees of 64 sociality in African mole-rats as in other rodents (Jarvis et al. 1994; Bennett et al. 1999; Firman 65 et al. 2020). Breeding in all solitary and some social African mole-rat species is seasonal, with 66 the activation of breeding coinciding with the increase in soil moisture content and the 67 sudden flushes of primary production, which occurs as a consequence of the onset of rainfall 68 (Jarvis 1969; Bennett and Jarvis 1988a; Bennett 1989; Spinks et al. 1997, 1999; Janse Van 69 Rensburg et al. 2002; Herbst et al. 2004; Hart et al. 2006). In contrast, the vast majority of the 70 social and eusocial African mole-rats species breed throughout the year (Bennett and Jarvis 71 1988b; Bennett and Aguilar 1995; Oosthuizen et al. 2008; Sichilima et al. 2011). © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 4 of 41 72 73 Social and eusocial bathyergids exhibit cooperative breeding and a reproductive division of 74 labour where reproduction is often monopolised by a single breeding female (BF) and one to 75 three of the largest males (breeding males: BMs) within the colony (Bennett and Faulkes 76 2000). The remaining colony members (non-breeding females – NBFs and non-breeding males 77 - NBMs) are reproductively quiescent, where both NBFs and NBMs can reproduce but are 78 naturally reproductively suppressed by the dominant breeding individuals (Bennett and 79 Faulkes 2000). This reproductive suppression can be physiological (Bennett et al. 2018; 80 Medger et al. 2019; Blecher et al. 2020) or behavioural (Burda 1995; Bennett et al. 1997; 81 Lutermann et al. 2013), or even a combination of the two (Bennett et al. 1996). The extent of 82 the suppression varies between the speciesDraft and the sexes (Bennett et al. 1996). Some non- 83 breeding colony members attempt to escape this suppression by dispersing and forming their 84 own colonies (Bennett and Faulkes 2000). Dispersal from the natal colony occurs under 85 favourable environmental conditions when the soil characteristics are optimal for excavation 86 and digging, such as periods of good rainfall (Jarvis et al. 1994; Molteno and Bennett 2002a; 87 Scantlebury et al. 2006). If rainfall controls dispersal periods, reproductive inhibition in non- 88 breeding colony members may be relaxed during these periods because of the greater 89 probability of successful independent reproduction (Molteno and Bennett 2002a). This 90 phenomenon of relaxation of suppression has been found in several social African mole-rat 91 species (Bennett 1989; Spinks et al. 1997, 1999; Janse Van Rensburg et al. 2002). 92 93 Even though extensive work has been conducted on the reproductive biology of African mole- 94 rat species, some sub-species in the genus Cryptomys have remained neglected. One such 95 sub-species is the social Mahali mole-rat (Cryptomys hottentotus mahali (Roberts, 1913), © The Author(s) or their Institution(s) Page 5 of 41 Canadian Journal of Zoology 96 which is found in the relatively semi-arid bushveld regions of Gauteng, North West Province 97 and the Northern Cape of South Africa (van Jaarsveld et al. 2019; Fagir et al. 2021; Wallace et 98 al. 2021). Previous studies that have focussed on the reproductive strategies of the various 99 sub-species of Cryptomys hottentotus have shown surprisingly varied results. For example, 100 the common mole-rat (C. h. hottentotus (Roberts, 1913)) (Bennett 1989; Spinks et al. 1997) 101 and highveld mole-rat (C. h. pretoriae (Roberts, 1913)) (Janse Van Rensburg et al. 2002) are 102 found in regions with seasonal climatic variations including seasonal rainfall which results in 103 both sub-species exhibiting a strongly seasonal reproductive pattern. In contrast, the Natal 104 mole-rat (C. h. natalensis (Roberts, 1913)), which also inhabits regions characterised by a 105 seasonal climate, but where rainfall can occur at any time of the year, is an aseasonal breeder 106 (Oosthuizen et al. 2008). The diverseDraft reproductive strategies of the Cryptomys sub-species 107 allows us to ask an important question: are seasonal climatic variations the root cause of the 108 varying reproductive strategies in African mole-rats and possibly other cooperative breeding 109 and social mammal species? Research on little-studied sub-species, such as the Mahali mole- 110 rat may allow us to answer this question. 111 112 The Mahali mole-rat shares a close genetic relatedness (Faulkes et al. 2004; Broekman et al. 113 2006) and a close distributional range as well as similar climatic conditions with those of the 114 highveld mole-rat, except that in the former sub-species temperature is on average 5°C 115 warmer and the area has 10% less humidity throughout the year (van Jaarsveld et al. 2019; 116 Fagir et al. 2021, Wallace et al. 2021). The Mahali and highveld mole-rat experience distinct 117 seasonal climates with wet, warm summers and cool, dry winters throughout their 118 distributional range. Since both species occur in close proximity to one another and are 119 phylogenetically closely related, we posited that the Mahali mole-rat should exhibit a similar © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 6 of 41 120 pattern of reproductive biology and strategies to that of the highveld mole-rat as described 121 in Janse Van Rensburg et al.

Load more