Age at first reproduction in wolves: different patterns of density dependence for females and males

Abstract

Age at first reproduction constitutes a key life-history trait in animals and is evolutionarily shaped by fitness benefits and costs of delayed versus early reproduction. The understanding of how intrinsic and extrinsic changes affects age at first reproduction is crucial for conservation and management of threatened species because of its demographic effects on population growth and generation time. For a period of 40 years in the Scandinavian wolf ( Canis lupus ) population, including the recolonization phase, we estimated age at first successful reproduction (pup survival to at least three weeks of age) and examined how the variation among individuals was explained by sex, population size (from 1 to 74 packs), primiparous or multiparous origin, reproductive experience of the partner and inbreeding. Median age at first reproduction was 3 years for females ( n = 60) and 2 years for males ( n = 74), and ranged between 1 and 8–10 years of age ( n = 297). Female age at first reproduction decreased with increasing population size, and increased with higher levels of inbreeding. The probability for males to reproduce later first decreased, reaching its minimum when the number of territories approached 40–60, and then increased with increasing population size. Inbreeding for males and reproductive experience of parents and partners for both sexes had overall weak effects on age at first reproduction. These results allow for more accurate parameter estimates when modelling population dynamics for management and conservation of small and vulnerable wolf populations, and show how humans through legal harvest and illegal hunting influence an important life-history trait like age at first reproduction.

Genetic signature of immigrants and their effect on genetic diversity in the recently established Scandinavian wolf population

“…The time to reach HW equilibrium may also have been affected by a change in generation time, e.g. due to the increased culling rate and faster turnover of breeding pairs during the study period (Liberg et al 2020; see also Wikenros et al 2021).…”

Whole-genome resequencing of temporally stratified samples reveals substantial loss of haplotype diversity in the highly inbred Scandinavian wolf population

“…This includes reduced litter size and/or juvenile survival (e.g., see Figs. 3 and 5 ; Wabakken et al 2001 ; Liberg et al 2005 ), age at first reproduction ( Wikenros et al 2021 ), as well as congenital anomalies ( Räikkönen et al 2006 ; 2013 ). It will be important in the future to monitor the spread of incoming haplotypes as well as to follow the survival of founder haplotypes.…”

“…For the remaining time period up until 2014, wolves were split in two temporal subgroups of equal sample size (i.e., 1994-2005 and 2006-2014). The birth year of individual wolves was estimated based on aging using one of three methods: (a) tooth root sectioning and counting cementum annulation (Landon et al 1998;Gipson et al 2000) at Matson's Laboratory (https://matsonslab.com/the-science/cementum-aging/); (b) ag-ing based on years of parental reproduction (Wikenros et al 2021); or (c) morphological determination of juveniles (<1 yr) at the postmortem using macroscopic analyses of dentition and identification of bone growth plates by radiography.…”

Wolf monitoring in Scandinavia: evaluating counts of packs and reproduction events

“…If a reproduction event would have been undetected in 2011, the year previous to the first confirmed reproduction event, the mother would be only 1 year old. Wolves are rarely reproducing during their first year (Medjo and Mech 1976, Kreeger 2003) and in Scandinavia these cases are so far exclusive to males (Wikenros et al 2021). Moreover, 2 of the fathers were identified from DNA in 2003 during the time of mating in February (Mech and Boitani 2003) inside or near the female territory, further supporting a case of polyandry in the territory.…”