Reproductive effort and success of males in scramble‐competition polygyny: Evidence for trade‐offs between foraging and mate search

Abstract

Patterns of male reproductive allocation provide insight into life-history characteristics. The trade-offs associated with resource and female group defence are well-defined. However, less is understood about trade-offs in species that practise scramble-competition polygyny, where successful strategies may favour competitive mate-searching rather than contest competition and fighting. White-tailed deer (Odocoileus virginianus) practise scramble-competition polygyny where solitary males search for and assess receptivity of females scattered across the landscape. Physically mature males are expected to do most of the breeding because of the high energetic costs of reproduction and high social status. However, young males may collectively sire one-third of offspring. To gain a better understanding of trade-offs associated with scramble-competition polygyny, we quantified metrics associated with reproductive effort and success. We quantified changes in body mass of harvested males, energetic costs of locomotion based on movements of GPS radiocollared males and timing of reproduction via temporal genetic parentage assignments. Young males (1.5 and 2.5 years old) sired offspring, but their mating success was mainly limited to peak rut, when most females were in oestrus. Furthermore, multiple paternity was common, indicating opportunistic reproduction. Reproductive effort, indexed by body mass loss, was highest in prime-age males (5.5-6.5 years old). Surprisingly, young and postprime males also exhibited significant body mass loss, indicative of investment in reproductive effort. Movement rates increased twofold to fourfold during rut as a function of mate search activities, but cost of locomotion would cause only about one-third of observed body mass loss. Because males are capital breeders, we infer most of body mass loss is due to reduced foraging. In scramble-competition polygyny, the repeated location of potential mates and assessment of their oestrous status appear to be important constituents of male mating strategies. Therefore, mating success may be influenced by time management and spatial memory, and not based solely on social dominance. Thus, reproductive effort should be greater for individuals capable of reducing time foraging. For those that cannot, opportunistic mating opportunities may arise when operative adult sex ratios are low. Our analyses reveal valuable insight into the trade-offs associated with scramble-competition polygyny.

Optimisation of energetic and reproductive gains explains behavioural responses to environmental variation across seasons and years

“…This approach meant that activity for mating is not mutually exclusive of that for foraging. Activity that capitalises on mating opportunities instead of foraging comes at the detriment of energy balance as there is insufficient energy intake to offset the cost of activity (Lescroël et al, 2010; Foley et al, 2018). In red squirrels, the late winter mating season is associated with elevated energy expenditure (Lane et al, 2010) and endocrine indications of stress and energy mobilisation (Boonstra et al, 2017).…”

One in the Hand Worth Two in the Bush? Reproductive Effort of Young Males Is Not Affected by the Presence of Adult Males

“…Young males expended reproductive effort (Figure 3), which is consistent with them taking advantage of a reproductive opportunity (Hogg and Forbes, 1997;Yoccoz et al, 2002;DeYoung et al, 2006;Foley et al, 2018). Despite the absence of an effect of adult males on reproductive expenditures of yearling males (Figure 3), lower reproductive effort by young males is likely a function of past selective pressures acting on post-rut survival and the continued need to grow to bolster reproductive success as adults.…”

“…Expenditures associated with the rut can result in males losing ≥ 25% of their body mass (McElligott et al, 2003). Though mass loss associated with rut has been proposed to be largely caused by increased reproductive activity, there also is pronounced hypophagia in some males (Miquelle, 1990;Willisch and Ingold, 2007;Mysterud et al, 2008a), which is consistent with the inability of activity alone to explain patterns of mass loss (McElligott et al, 2003;Foley et al, 2018). Regardless, the substantial reproductive effort (e.g., reductions in forage intake, loss in somatic reserves) results in males exhibiting reductions in nutritional condition following the mating season (Yoccoz et al, 2002;Mysterud et al, 2003) and potentially negative effects to survival during the ensuing winter (Clutton-Brock, 1982;Stevenson and Bancroft, 1995;Ditchkoff et al, 2001).…”

Seasonal flooding effects on deer in the Mississippi river batture

“…Although winter flooding apparently provided long‐term benefits from silt deposition, winter flooding did not negatively affect current‐year antler growth. The post‐rut period is a critical time for males, which commonly lose >20% of body mass during the mating season (Strickland et al , Foley et al ), and antler growth may be correlated with body condition during the period of initiation (Gaspar‐López et al , Gómez et al , Dryden ). Supplemental feeding is legal in Louisiana and Mississippi and may have been a factor mitigating flooding effects.…”

“…Although winter flooding apparently provided long-term benefits from silt deposition, winter flooding did not negatively affect current-year antler growth. The post-rut period is a critical time for males, which commonly lose >20% of body mass during the mating season (Strickland et al 2017, Foley et al 2018, and antler growth may be correlated with body condition during the period of initiation (Gaspar-López et al 2010, Gómez et al 2012, Dryden 2016 Figure 6. Long-term trends for A) harvest rate, B) yearling female dressed body mass (with SE bars), and C) proportion of property planted in soybeans for 61 properties in the Mississippi River Batture region, USA, 1994-2016.…”