Measures of breeding inequality: a case study in southern elephant seals

Abstract

Inequality in distribution of resources is a key aspect of evolutionary biology particularly in relation to distribution of mates and copulations. Notwithstanding its important role, inequality is not easily defined, and its measurement is complicated by theoretical and methodological issues. Although the formal treatment of inequality has been mostly limited to the evolution of lek mating system, a methodologically correct approach to measurement of inequality is generally valid for the study of any kind of mating system. In this paper, we analyze inequality in a large set of southern elephant seal (Mirounga leonina) harems. The observed distribution of fertilizations was significantly different from both the expected distribution with equal shares of resources and the expected distribution with equal propensities to acquire resources. We calculate and compare various measures of inequality, observing a wide variation particularly among unbounded and bounded indices. We check the effect of choosing a specific measure of inequality by considering the effect of two aspects of harem socionomy, the number of females in the harem (i.e., the total amount of resources to be shared) and the number of males associated with the harem (i.e., the number of competitors). The choice of a specific measure of inequality had a strong impact on the results obtained and should be considered a critical step in every study of functional and evolutionary correlates of inequality. Unbounded indices showed a strong relationship with both harem size and number of males, while no effect was evident in the analysis of bounded indices. This demonstrates that, in this species, the despotism of the mating system remains high even in large harems and with many competitors, i.e., the worst conditions for monopolization.Résumé : L'inégalité dans la répartition des ressources, particulièrement la répartition des partenaires sexuels et des accouplements, est l'un des facteurs clés de la biologie évolutive. Malgré son rôle important, l'inégalité est difficile à dé-finir et à mesurer à cause de problèmes théoriques et méthodologiques. À ce jour, l'inégalité a été étudiée surtout dans le contexte de l'évolution du système d'accouplement sur leks; une approche méthodologiquement correcte de la mesure de l'inégalité devrait être valide pour l'étude de n'importe quel système d'accouplement. Nous analysons ici l'inégalité au sein d'une grande série de harems d'éléphants de mer (Mirounga leonina). La répartition observée des fé-condations diffère significativement de la répartition théorique prévue lorsque les ressources sont réparties également et diffère aussi de la répartition à laquelle on peut s'attendre lorsque les animaux ont tous la même propension à chercher à obtenir la ressource. Nous calculons et comparons diverses mesures de l'inégalité et obtenons une grande variation, particulièrement entre les indices non bornés et les indices bornés. Nous vérifions les effets du choix d'une mesure spécifique de l'inégalité en tenant compte de deux aspect...

Observational Evidences of Vocal Learning in Southern Elephant Seals: a Longitudinal Study

“…Male elephant seals differ greatly in reproductive success within and across breeding seasons and on a lifetime basis (Le Boeuf & Reiter 1988). At Sea Lion Island, variation in mating success across males is the highest ever recorded for a vertebrate (Galimberti et al 2002), and is reflected in the distribution of true genetic paternities (Fabiani et al 2004). Dominance hierarchies show strong linearity , and access to females is related strictly to competitive success and dominance rank.…”

“…Northern ( M. angustirostris ) and southern elephant seals are the most polygynous of all mammals, with a mating system based on harems (i.e. female‐defence polygyny) and strong competition among males for access to females (Galimberti et al. 2002).…”

“…Northern (M. angustirostris) and southern elephant seals are the most polygynous of all mammals, with a mating system based on harems (i.e. female-defence polygyny) and strong competition among males for access to females (Galimberti et al 2002). Male elephant seal agonistic vocalizations are one of the most important components of inter-male competition, and likely function to communicate information about the resource-holding potential of the emitter (Bartholomew & Collias 1962;Shipley et al 1981Shipley et al , 1986Sanvito & Galimberti 2003).…”

Creation Nerves of the Lumbar and Sacral Plexus in California Sea Lions (Zalophus Californianus) and Northern Elephant Seals (Mirounga Angustirostris)/Formiranje Nerava Iz Lumbalnog I Sakralnog Pleksusa Kod Kalifornijskog Morskog Lava (Zalophus Californianus) I Severnomorskog Slona (Mirounga Angustirostris)

“…Numerous investigations [17][18][19][20][21] of pinnipedia in that respect were associated with depth and duration of diving, as well as with the changes occurring in different organ systems during diving. Some authors [22][23][24][25][26][27] chose to investigate the behavior, growth and development of different species of sea lions. Genetic variability was also investigated in some pinnipedia [26,[28][29][30].…”

“…Some authors [22][23][24][25][26][27] chose to investigate the behavior, growth and development of different species of sea lions. Genetic variability was also investigated in some pinnipedia [26,[28][29][30]. However, very few authors investigated their nervous system, especially the peripheral nervous system.…”