Predictive capacity of boar sperm morphometry and morphometric sub-populations on reproductive success after artificial insemination

The aim of the study was to compare the morphometric features of sperm head size and shape from the Pietrain line and the Duroc × Pietrain boar crossbred terminal lines, and to evaluate their relationship with reproductive success after artificial insemination of sows produced from crossbreeding the York, Landrace and Pietrain breeds. Semen samples were collected from 11 sexually mature boars. Only ejaculates with greater than 70% motility rate and <15% of abnormal sperm were used for artificial inseminations (AI) and included in the study. Samples were analyzed using an ISAS®v1 computer-assisted sperm analysis system for eight morphometric parameters of head shape and size (CASA-Morph). Sub-populations of morphometric ejaculates were characterized using multivariate procedures, such as principal component (PC) analysis and clustering methods (k-means model). Four different ejaculate sub-populations were identified from two PCs that involved the head shape and size of the spermatozoa. The discriminant ability of the different morphometric sperm variables to predict sow litter size was analyzed using a receiver operating characteristics (ROC) curve analysis. Sperm head length, ellipticity, elongation, and regularity showed significant predictive capacity on litter size (0.59, 0.59, 0.60, and 0.56 area under curve (AUC), respectively). The morphometric sperm sub-populations were not related to sow litter size

Mate availability affects the trade-off between producing one or multiple annual clutches

Females of many iteroparous species face trade-offs between producing one or multiple broods per reproductive season, and over fertilizing broods with sperm from the same or different mates. Both trade-offs might be affected by the availability of males (i.e. absence/presence of males) and the timing and duration of male encounter. Here, we experimentally manipulated the duration of mate availability at the first brood and mate availability per se (i.e. absence/presence of mates) at the second brood, and tested their effects on female and male reproductive success, using the common lizard, Zootoca vivipara, as a model species. Females were either exposed to males for a long time-span before their first annual reproduction and they could re-mate before their second annual reproduction (unrestricted treatment). Alternatively, they were exposed to males for a short time-span before their first annual reproduction and they were not allowed to re-mate (restricted treatment). Reproductive success of first clutches was not directly affected by the duration of access to males. Re-mating positively affected the probability of producing a second clutch, and the proportion of viable offspring. Re-mating by females also affected the reproductive success of males: fewer second clutch eggs were fertilized with stored sperm in unrestricted compared to restricted females. Sperm presence in males was high until the end of the re-mating period. Our results suggest a close coevolution between male and female reproductive strategies and they point to facultative skipping of second broods, when fitness benefits are small. This shows that behavioural strategies are at least partially responsible for the production of multiple annual broods. The detected behavioural strategies are likely widespread, given the multitude of taxa raising multiple broods in some, but not all years, and given that in most taxa some, but not all individuals, produce multiple annual broods

Intra-individual variation in sperm tail length in murine rodents

The definitive version is available at www.blackwell-synergy.comIn eutherian mammals, there are marked interspecific differences in sperm head shape and tail length. In a few species, sperm head variability occurs but intra-individual variation in sperm tail length has rarely been investigated or commented upon. Here, we ask the question: Do murine rodent species that have variable sperm head shapes exhibit greater intra-individual variation in sperm midpiece and total tail lengths than closely related species where little, or no, sperm head variability occurs? From three separate lineages, we selected three pairs of murine rodents, one of which has monomorphic, and the other variable, sperm head shape. These were from southern Asia the bandicoot rats Bandicota bengalensis and Bandicota indica, from southern Africa the veld rats, Aethomys chrysophilus and Aethomys ineptus and from Australia the fawn hopping mouse Notomys cervinus and the spinifex hopping mouse Notomys alexis. Cauda epididymal sperm smears were prepared and sperm midpiece and total tail lengths were determined. A linear mixed-effects model was used to estimate intra-individual variance. The results showed that in all three species where there are variable sperm head shapes (B. indica, A. ineptus and N. alexis), statistically significantly greater intra-individual variability of sperm midpiece and total tail lengths occurs (P<0.0001 in all cases). These species all have relatively smaller testes mass compared with the closely related species with monomorphic sperm populations. This suggests that depressed levels of intermale sperm competition may result in the occurrence of variability in not only the divergent sperm head shape but also in the length of the midpiece as well as that of the total length of the sperm tail.W. G. Breed, M. Bauer, R. Wade, N. Thitipramote, J. Suwajarat, L. Yellan