Capital-Income Breeding in Male Ungulates: Causes and Consequences of Strategy Differences Among Species

Abstract

The capital and income breeding concept links energy resources used during reproduction to the timing of their acquisition. During reproduction, capital breeders rely on resources gained previously and accumulated for reproductive investment. By contrast, income breeders use mainly resources collected during the period of reproductive activity. Most commonly, this concept is applied to females; relatively few studies have considered males. Moreover, there has been little attention to the link between the capital-income divide and other aspects of mating strategy. We studied adult males of three wild ungulates with different levels of polygyny. A large dataset (4,264 red deer, 53,619 roe deer, and 13,537 Alpine chamois, respectively) was obtained during 2007-2017 in the whole territory of Slovenia and in the Trento province, Italy. During the rut, body mass loss of males in highly polygynous species was more than twice that of weakly polygynous species: on average, red deer stags lost 19.5%; chamois bucks 16.0%; and roe deer bucks 7.5% of their body mass. This indicates potential for a hitherto unrecognized link between the degree of intrasexual competition and the degree of capital mating. The variability in body mass at the end of the rut was clearly reduced in both highly polygynous species (from 15.1 to 9.4% in red deer, and from 12.5 to 10.5% in chamois), but did not change in roe deer. Finally, roe deer bucks had recovered body mass to that of the pre-rut period by just 2 months after the rut, while red deer stags did not manage to compensate the loss of weight until the end of the year. We suggest that, at least in ungulates, there is a link between the degree of polygyny and that of capital breeding. Males of capital and income breeders underwent body mass changes resulting from different reproductive investment during the rut. Capital breeders lost considerably more weight, and invested a variable amount of energy among individuals or among years, possibly to cope with different environmental or body conditions. In so doing, they ended the rut with poorer but more even condition among individuals.

Capital-income breeding in wild boar: a comparison between two sexes

“…If the relation between body weight loss and conception event distribution had remained the same as it was observed during the sampling period, we can estimate that adult males would have lost 16.57 ± 1.39% of their pre-reproductive body weight by the end of the rut. Adult male wild boar relative weight loss estimated by our analysis can be compared with that of male Alpine chamois ( Rupicapra rupicapra rupicapra , 17–19% in Mason et al 16 and 16.0% in Apollonio et al 6 ) and male red deer ( Cervus elaphus , 19.5% in Apollonio et al 6 ), which are usually considered capital breeders 6 , 14 . Accordingly, our results position adult male wild boar towards the capital end of the capital-income breeding continuum.…”

“…Larger body size can facilitate capital breeding on account of a lower relative cost for reserve transportation and a higher metabolism efficiency 3 . The mating system and, specifically, the degree of polygyny may act as a further push-factor in positioning male ungulates along the capital-income continuum 6 . Indeed, higher levels of intra-sexual male competition for mating opportunities are likely to enhance the reproductive demands of polygynous males and, concomitantly, their tendency to adopt feeding reduction 7 , 8 and suppression 9 , 10 during the rut, inevitably forcing them to rely on a stored capital of reserves.…”

“…The relatively high degree of polygyny of this species 17 entails high competition among males for mating opportunities. This may be expected to increase both the need and the potential reproductive value of relying on stored reserves and thus promote capital breeding 6 . In addition, the gregarious habits of females 27 and the high litter size 28 make male reproductive effort even more beneficial in terms of potential number of descendants, thus exacerbating intra-male competition.…”

First Insights into the Population Genetic Structure and Heterozygosity–Fitness Relationship in Roe Deer Inhabiting the Area between the Alps and Dinaric Mountains

“…Roe deer is a typical income breeder with few available body reserves [29]. Therefore, its body mass shows relatively low seasonality; for example, adult males experience much lower rut-related loss of body mass (7.5%) than their counterparts in capital breeders, such as red deer or chamois [30]. In consequence, roe deer body mass is a relevant proxy for an individual's condition and phenotypic quality [107].…”

“…As roe deer are income breeders [29], their body mass shows a relatively low seasonality due to investment in reproduction; indeed, during the rut, roe deer males lose on average only 7.5% of body mass compared to 19.5% in red deer (Cervus elaphus) and 16.0% in chamois (Rupicapra rupicapra) [30]. Therefore, roe deer body mass can serve as a proxy for an individual's general fitness, and is of crucial importance for the reproductive success of the species (reviewed in [31,32]).…”