Demographic, environmental and genetic determinants of mating success in captive koalas (Phascolarctos cinereus)

Abstract

Many factors have been shown to affect mating behavior. For instance, genes of the major histocompatibility complex (MHC) are known to influence mate choice in a wide variety of vertebrate species. The genetic management of captive populations can be confounded if intrinsic mate choice reduces or eliminates reproductive success between carefully chosen breeding pairs. For example, the San Diego Zoo koala colony only has a 45% copulation rate for matched individuals. Herein, we investigated determinants of koala mating success using breeding records and genotypes for 52 individuals at four MHC markers. We quantified MHC diversity according to functional amino acids, heterozygosity, and the probability of producing a heterozygous offspring. We then used categorical analysis and logistic regression to investigate both copulation and parturition success. In addition, we also examined age, day length, and average pairwise kinship. Our post-hoc power analysis indicates that at a power level of 1−β = 0.8, we should have been able to detect strong MHC preferences. However, we did not find a significant MHC effect on either copulation or parturition success with one exception: pairs with lower or no production of a joey had significantly lower MHC functional amino acid diversity in the categorical analysis. In contrast, day length and dam age (or age difference of the pair) consistently had an effect on mating success. These findings may be leveraged to improve the success of attempted pairs, conserve resources, and facilitate genetic management. K E Y W O R D Scopulation, day length, female choice, major histocompatibility complex, parturition

High-throughput immunogenetic typing of koalas suggests possible link between MHC alleles and cancers

“…All of the expressed MHC class I genes appear to be present as single copy genes in the genome (Cheng et al 2018 ; Johnson et al 2018 ). Within the MHC class II gene family, four class II subfamilies are recognized, consisting of alpha and beta subunits of DA, DB, DC and DM (Abts et al 2018 ; Johnson et al 2018 ; Lau et al 2013 ). Studies investigating the allelic diversity of class II DA and DB genes have found that the beta subfamilies (DAB and DBB) contain more allelic diversity than the alpha subfamilies (DAA and DAA) (Lau et al 2013 ).…”

“…While this approach improved throughput, it could not guarantee every allele for a tested gene was detected in the set of sequenced clones. Most recently, direct Illumina sequencing of PCR amplicons from the target loci was attempted for a range of class I and II gene loci (Abts et al 2018 ). This approach allowed for higher throughput processing and greatly increased confidence that all the allelic diversity within a koala would be detected; however, sequence processing challenges related to amplicon size and multiple genes per loci limited the number of targets that generated reportable data.…”

The establishment of a Living Genome Resource Bank utilising genetic analysis and assisted breeding technology: a case study on the koala (Phascolarctos cinereus)

“…Further, a 2018 study on captive koala mating success determined that the average joey success rate (i.e. joey maintained until emergence) in captive females is 44% (Abts et al, 2018). This study reports a higher joey success rate of 58.3% (± 20.4), which might reflect the rate of inbreeding within the captive population, or non-genetic factors such as the environment or koala management.…”

“…The breeding records for the captive female koalas (n= 23) included details on every mating performed by that koala and whether a joey resulted. These data were then correlated to joey records, which outlined when each koala was in the emergence stage of being weaned from its mother, to date (or up until death), as per the methodology outlined by Abts et al (2018). Therefore, the fitness trait representing female reproductive capacity used in this analysis was the percentage of joey success, defined as the number of joeys weaned per number of attempted matings.…”

“…Multiple studies have demonstrated HFCs related to male fertility as an increase in the percentage of abnormal spermatozoa associated with low heterozygosity in species such as: Homo sapiens (Baccetti et al, 2001;Bishop, 1972;Moretti and Collodel, 2005); bulls (Bos Taurus) (Chandler and Adkinson, 1990;Chenoweth, 2005;Salisbury and Baker, 1966); the Mohor gazelle (Gazella dama mhorr) and the Iberian lynx (Lynx pardinus) (Ruiz-López et al, 2012). Unfortunately, due to the internal nature of the female reproductive system, it is difficult to so easily evaluate any abnormalities in live females, and so studies on female fitness have focused on fecundity in terms of number of successfully weaned offspring, such as the studies conducted on the blue tit (Cyanistes caeruleus) (Olano-Marin et al, 2011) and the koala (Abts et al, 2018).…”