Male Elephant Seals Research Articles

The ontogeny of at-sea behaviour in male southern elephant seals (Mirounga leonina) at Marion Island

Megafauna, such as southern elephant seals (SESs) (Mirounga leonina, Linn.), forage in diverse, seemingly limitless habitats. In pelagic settings, their behaviour is more likely to be limited by physiological ability and prey distribution, than physical barriers. For elephant seals, their rapid growth in body size corresponds to changing physiological abilities. These changes are most pronounced for male elephant seals. While most studies have compared male and female SESs in terms of changing body size and physiological ability, few studies have compared the influence of changing body size on behaviour of male SESs from the same population using long term satellite tracking data. We describe age-related differences in movement and diving behaviour for male SESs from Marion Island. We analysed satellite tracking data collected from 23 male SESs seals fitted with Sea Mammal Research Unit Satellite Relay Data Loggers at Marion Island between 2005 and 2011. Each dive was assigned a behavioural mode, either ‘searching’ or ‘transit’, using state-space modelling. We used mixed-effects models to quantify the influence of age and behavioural mode on dive duration, surface duration, dive depth and number of daily dives. Younger seals travelled significantly further from Marion Island and spent most of their dives in transit mode, whereas older seals stayed closer to the island but were in searching mode for most of their tracks. When searching, older seals dived more frequently, displayed longer dive and surface durations, and reached greater depths than younger seals. These differences in diving behaviour seem to reflect changing physiological ability. For male SESs, changes in physiological ability necessitate behavioural plasticity, which may be the key to survival and future breeding success. Robust males are more likely to breed and must therefore, maintain their body size by adapting to local oceanic conditions.

Selective disappearance of frail juveniles: consequences for understanding social dominance in adult male elephant seals

Individual heterogeneity is variation in trait expression observed among individuals of a population. Individual heterogeneity in the pre‐breeder stage of development is of importance given its eventual contribution to the breeding population's overall reproductive performance. Yet most studies do not consider the role of individual heterogeneity in pre‐breeders when investigating population processes. We investigated individual heterogeneity in the survival and recruitment probabilities of pre‐breeding male southern elephant sealsMirounga leoninausing 34 years of data collected at Marion Island. Elephant seals are highly polygynous capital breeders, with few male offspring surviving to compete in breeding events and even fewer breeding successfully. Specifically, we fitted finite‐mixture models with two hidden groups that represented ‘robust’ and ‘frail’ individuals and compared the demographic rates of these groups to that of the population. Survival and recruitment as first‐time subordinate breeders could be distinguished between groups. Survival of both robust and frail pre‐breeders decreased from age 2, whilst differences between groups were maintained (ontogeny processes). Frail pre‐breeders had a much lower survival than the population average, suggesting that frail individuals were preferentially removed from the population (selective disappearance). Differences in recruitment probabilities were apparent from age 5 (earliest recorded age) and increased until age 7, with most recruits comprising robust pre‐breeders. Male pre‐breeders were more likely to be robust at age 2 when born in years with few conspecifics, suggesting that individual heterogeneity was determined, in part, by density‐dependent effects. A population projection model revealed that male breeders of every age class never consisted of more than 5% of frail recruits. Rather, the breeding population increasingly consisted of robust recruits that obtained social dominance with age. We demonstrated that individual heterogeneity in male pre‐breeder demographic rates was present and persistent throughout much of development and determined the proportion of adult males that obtained social dominance.

Mummified and skeletal southern elephant seals (Mirounga leonina) from the Victoria Land Coast, Ross Sea, Antarctica

AbstractWe report on an accumulation of mummified southern elephant seals (Mirounga leonina) from Inexpressible Island on the Victoria Land Coast (VLC), western Ross Sea, Antarctica. This accumulation is unusual, as elephant seals typically breed and molt on sub‐Antarctic islands further north and do not currently occupy the VLC. Prior ancient DNA analyses revealed that these seals were part of a large, Antarctic breeding population that crashed ~1,000 yr ago. Radiocarbon dates for Inexpressible Island mummies range from 380 to 3,270 yr before present, too old to have been created by Scott's Northern Party in 1912 and varying too widely in age to represent a catastrophic death assemblage. Skeletal measurements reveal that most Inexpressible Island mummies are adult or subadult males. The presence of male elephant seals on Inexpressible Island until several hundred years ago suggests that, at a minimum, it served as a haul‐out site for the large Antarctic population and may have hosted a breeding colony. The conditions that allowed this Antarctic population to use the Ross Sea, the factors spurring its decline, and the implications for the adaptability and sensitivity of the species to environmental change all merit further study.

Fasting increases the phosphorylation of AMPK and expression of sirtuin1 in muscle of adult male northern elephant seals ( Mirounga angustirostris )

Fasting typically suppresses thyroid hormone (TH)‐mediated cellular events and increases sirtuin 1 (SIRT1) activity. THs may regulate metabolism through nongenomic pathways and directly through activation of adenosine monophosphate‐activated protein kinase (AMPK). Adult male elephant seals (Mirounga angustirostris) are active, hypermetabolic, and normothermic during their annual breeding fast, which is characterized by stable TH levels. However, the contribution of TH to maintenance of their fasting metabolism is unknown. To investigate the fasting effects on cellular TH‐mediated events and its potential association with SIRT1 and AMPK, we quantified plasma TH levels, mRNA expressions of muscle SIRT1 and TH‐associated genes as well as the phosphorylation of AMPK in adult, male northern elephant seals (n = 10/fasting period) over 8 weeks of fasting (early vs. late). Deiodinase type I (DI1) expression increased twofold with fasting duration suggesting that the potential for TH‐mediated cellular signaling is increased. AMPK phosphorylation increased 61 ± 21% with fasting suggesting that cellular metabolism is increased. The mRNA expression of the TH transporter, monocarboxylate transporter 10 (MCT10), increased 2.4‐fold and the TH receptor (THrβ‐1) decreased 30‐fold suggesting that cellular uptake of T4 is increased, but its subsequent cellular effects such as activation of AMPK are likely nongenomic. The up‐regulation of SIRT1 mRNA expression (2.6‐fold) likely contributes to the nongenomic activation of AMPK by TH, which may be necessary to maintain the expression of PGC‐1α. These coordinated changes likely contribute to the up‐regulation of mitochondrial metabolism to support the energetic demands associated with prolonged fasting in adult seals.

Variation in the diet of killer whales Orcinus orca at Marion Island, Southern Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 549:263-274 (2016) - DOI: https://doi.org/10.3354/meps11676 Variation in the diet of killer whales Orcinus orca at Marion Island, Southern Ocean Ryan R. Reisinger1,5,*, Darren R. Gröcke2, Nico Lübcker1, Erin L. McClymont3, A. Rus Hoelzel4, P. J. Nico de Bruyn1 1Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, Pretoria, South Africa 2Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, UK 3Department of Geography, Durham University, South Road, Durham DH1 3LE, UK 4School of Biological and Biomedical Sciences, Durham University, South Road, Durham DH1 3LE, UK 5Present address: Department of Zoology, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa *Corresponding author: ryan.r.reisinger@gmail.com ABSTRACT: Diet seems to be a key factor driving diversity and isolation among killer whale populations. Killer whales at Marion Island, Southern Ocean, have been observed preying on seals and penguins but are also know to depredate Patagonian toothfish from longline fishing vessels. However, their diet is poorly known especially when they occur offshore. We analysed carbon and nitrogen stable isotope ratios in 32 skin samples collected from 24 killer whales belonging to 8 social units. Adult males showed higher δ15N values than adult females or subadults, indicating that they occupy a higher relative trophic level. There were no significant differences in δ13C among social units, but δ15N differed significantly and 2 individuals from social units which have been observed depredating Patagonian toothfish had higher δ15N values. The inshore presence of killer whales at Marion Island was a significant predictor of δ13C values, but not of δ15N values. This suggests some foraging north of Marion Island, potentially on lower trophic level prey. We also analysed tissue samples from seal, penguin and Patagonian toothfish prey and used available values for Antarctic fur seals. Results show that killer whales around Marion Island are apex predators, but that they do not feed exclusively on other high trophic level predators such as elephant seals, fur seals, and Patagonian toothfish. Killer whales had δ15N values similar to those of Patagonian toothfish and adult male elephant seals, implying that the diet of killer whales at Marion Island includes some lower trophic level prey such as cephalopods or fishes. KEY WORDS: Predator · Stable isotopes · Carbon · δ13C · Nitrogen · δ15N · Foraging · Trophic level Full text in pdf format Supplementary material PreviousNextCite this article as: Reisinger RR, Gröcke DR, Lübcker N, McClymont EL, Hoelzel AR, de Bruyn PJN (2016) Variation in the diet of killer whales Orcinus orca at Marion Island, Southern Ocean. Mar Ecol Prog Ser 549:263-274. https://doi.org/10.3354/meps11676 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 549. Online publication date: May 10, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Why males and females look different

Why do males and females look different? In “Odd Couples: Extraordinary Differences Between the Sexes in the Animal Kingdom,” (2013, Princeton University Press, p. 312), Daphne J. Fairbairn provides a scrupulous catalog of possible answers, perhaps the most detailed collection of animal sex differences since Darwin’s 1874 “The Descent of Man and Selection in Relation to Sex.” Sexual dimorphism is the condition in which males and females exhibit distinct phenotypes, beyond physiological traits involved with reproduction. Fairbairn’s volume is supplied with some of the best examples of such differences now known, and the disparate sources of data are pressed into compelling shape by a talented scholar and careful experimentalist. Fairbairn’s manifesto is, “an overtly Darwinian approach to understanding sexual differences” (p. 3). She notes that when selection operates in sex-specific ways, “we expect trait distributions typical for each sex to be adaptive for that sex” (p. 4), and she launches the reader into this view of dimorphism with sweeping taxonomic and gender-modified scope. We learn of lumbering male elephant seals, who in the throes of their ardor may annihilate the offspring of their future mates; of great bustards, giant Eurasian cranes whose males shove rivals and take blows to the face like bear-pit pugilists while females watch nearby; of shellcarrying cichlid fish, whose territorial and satellite males dart and parry for opportunities to ejaculate into snail shells containing females’ unfertilized ova. As vertebrates, we humans are most familiar with mating systems in which males are larger or somehow more elaborate than females. Fairbairn answers this preexisting bias with fascinating contrasts, weaving tales of yellow garden spiders and blanket octopus, whose gigantic females either squat in the center of conspicuous webs, or float huge and enigmatic over tropical reefs, each attended by males of their species as much as 40,000 times smaller in size. We learn of giant seadevil anglerfish, whose enormous, fang-jawed females host tiny males, who cling to female undersides by their own peculiar mouths, absorbing nutrients from a shared bloodstream and dangling close enough to their mate’s genitalia to ensure successful spawning. Fairbairn details the divergent life histories of bizarre, deep-sea bone worms whose females embed their bulbous bodies within decaying skeletons of whales, and maintain hundreds of minute suitors within their translucent skins. Lastly, she describes shell-burrowing barnacles, in which embedded females may (or may not—45% of females fail to mate) host posses of minuscule males with colossal, inflatable penises that may exceed each little fellow’s corporal dimensions by as much as eight times. The density of information and much delightful prose make this a fascinating read for lay and professional readers alike. Footnotes and appendices comprise nearly one-third of the book. One diagram describes the distribution of sexual dimorphism among 73 animal classes, a synthesis across 1.4 million species that is the first I have seen of its kind. Fairbairn glides among the animals with remarkable skill, and does Darwin one better with abundant recent data. In each chapter, she recounts male and female life spans, the fractions of individuals who do and do not mate, and the numbers of offspring that individuals in each sex produce. The raw materials are here to make concise, quantitative statements about how a sex difference in the variance in relative fitness (also known as the opportunity for sexual selection; Wade 1979) can explain the magnitude and direction of sexual dimorphism. But each chapter ends without an attempt. Offspring numbers are what Fairbairn considers “the currency of Darwinian fitness,” yet the trove of such information presented is used mainly for implication. Fairbairn concludes, “the enduring message is that there is no one way of being a male or a female animal . . . there is no “normal” or “typical” pattern of sexual differentiation across the animal kingdom,” and furthermore that the lack of sex differences in externally fertilizing species “remains a mystery” (p. 165). I found such capitulation

Oxidative stress is a potential cost of breeding in male and female northern elephant seals.

The trade-off between current reproductive effort and survival is a key concept of life history theory. A variety of studies support the existence of this trade-off but the underlying physiological mechanisms are not well-understood. Oxidative stress has been proposed as a potential mechanism underlying the observed inverse relationship between reproductive investment and lifespan. Prolonged fasting is associated with oxidative stress including increases in the production of reactive oxygen species, oxidative damage and inflammation.Northern elephant seals (NES) undergo prolonged fasts while maintaining high metabolic rates during breeding. We investigated NES of both sexes to assess oxidative stress associated with extended breeding fasts. We measured changes in the plasma activity or concentrations of markers for oxidative stress in 30 adult male and 33 adult female northern elephant seals across their 1-3 month breeding fasts. Markers assessed included a pro-oxidant enzyme, several antioxidant enzymes, markers for oxidative damage to lipids, proteins and DNA, and markers for systemic inflammation.Plasma xanthine oxidase (XO), a pro-oxidant enzyme that increases production of oxidative radicals, and several protective antioxidant enzymes increased over breeding in both sexes. Males showed increased oxidative damage to lipids and DNA and increased systemic inflammation, while oxidative damage to proteins declined across breeding. In contrast, females showed no oxidative damage to lipids or DNA or changes in inflammation, but showed increases in oxidative damage to proteins. XO activity, antioxidant enzymes, oxidative damage markers, and inflammatory markers were strongly correlated in males but these relationships were weaker or non-existent in females.NES provide evidence for oxidative stress as a physiological cost of reproduction in a capital breeding mammal. Both sexes strongly up-regulated antioxidant defenses during breeding. Despite this response, and in contrast to similar duration non-breeding fasts in previous studies on conspecifics, there was evidence of oxidative damage to tissues. These data demonstrate the utility of using plasma markers to examine oxidative stress but also suggest the necessity of measuring a broad suite of plasma markers to assess systemic oxidative stress.

Elephant seals' CO as high as heavy human smokers'

![Figure][1] Two adult male elephant seals. Photo credit: Michael Tift. Carbon monoxide (CO) is a silent killer. Produced by incomplete combustion, the colourless, odourless gas binds to the oxygen carrying protein – haemoglobin – in the blood of smokers and fire victims, insidiously

Deep divers in even deeper seas: habitat use of male southern elephant seals from Marion Island

AbstractWe describe the habitat use of 22 male southern elephant seals (Mirounga leonina) satellite tagged at Marion Island between 2004 and 2008. While a few areas of increased utilization appeared to be associated with areas of shallower bathymetry (such as sea-floor ridges and fracture zones), seals in our study did not target other areas of shallow bathymetry within close proximity to Marion Island. Rather, most elephant seals foraged pelagically over very deep water where much variation was evident in diel vertical migration strategies. These strategies resulted in generally deeper and longer dives than what has been reported for male elephant seals from other colonies. No significant differences were recorded for dive durations or dive depths between adults and sub-adults. However, younger animals displayed a positive relationship between dive durations and age, as well as between dive depths and age, while these relationships became negative for older animals. Mixed model outputs suggested that seals increased their aerobic fitness as migrations progressed, enabling them to undertake longer dives. We conclude that Marion Island male elephant seals exhibit much variability in dive strategy and are seemingly capable of exploiting a range of different prey types occurring in various depth layers.

Inter-population differences in diving behaviour of adult male southern elephant seals (Mirounga leonina)

Access to different environments may lead to inter-population behavioural changes within a species that allow populations to exploit their immediate environments. Elephant seals from Marion Island (MI) and King George Island (KGI) (Isla 25 de Mayo) forage in different oceanic environments and evidently employ different foraging strategies. This study elucidates some of the factors influencing the diving behaviour of male southern elephant seals from these populations tracked between 1999 and 2002. Mixed-effects models were used to determine the influence of bathymetry, population of origin, body length (as a proxy for size) and individual variation on the diving behaviour of adult male elephant seals from the two populations. Males from KGI and MI showed differences in all dive parameters. MI males dived deeper and longer (median: 652.0 m and 34.00 min) than KGI males (median: 359.1 m and 25.50 min). KGI males appeared to forage both benthically and pelagically while MI males in this study rarely reached depths close to the seafloor and appeared to forage pelagically. Model outputs indicate that males from the two populations showed substantial differences in their dive depths, even when foraging in areas of similar water depth. Whereas dive depths were not significantly influenced by the size of the animals, size played a significant role in dive durations, though this was also influenced by the population that elephant seals originated from. This study provides some support for inter-population differences in dive behaviour of male southern elephant seals.

High-density lipoprotein remains elevated despite reductions in total cholesterol in fasting adult male elephant seals (Mirounga angustirostris)

We examined changes in lipid profiles of 40 adult northern elephant seal bulls over the 3-month breeding fast and the 1-month molting fast to investigate impacts of fasting on serum total cholesterol (TC), triglycerides (TG) and lipoproteins. Total cholesterol and low-density lipoprotein (LDL) levels were initially high (3930 ± 190mgL(-1)and 1610 ± 170mgL(-1), respectively) and decreased significantly over the breeding season. Total cholesterol and LDL declined significantly with adipose tissue reserves (p<0.001), and LDL levels as low as 43 mgL(-1) were measured in seals late in the breeding fast. Less dramatic but similar changes in lipid metabolism were observed across the molting fast. High-density lipoproteins (HDL) remained consistently elevated (>1750 mgL(-1)) suggesting that elephant seals defend HDL concentrations, despite significant depletion of TC and LDL across the breeding fast. Triglyceride levels were significantly higher during the molt, consistent with lower rates of lipid oxidation needed to meet metabolic energy demands during this period. The maintenance of HDL during breeding is consistent with its role in delivering cholesterol from adipose tissue for steroidogenesis and spermatogenesis and potentially mitigates oxidative stress associated with fasting.

Directionality of male northern elephant seal (Mirounga angustirostris) threat calls and how it influences receiver behavior.

Many animal sounds are directional in which the sound energy is focused in a direction that depends on the signaler’s orientation. In the 1970s, Ron Schusterman quantitatively showed this in barking California sea lions and dogs. Several investigators have suggested ways that such features might be particularly useful among individuals in acoustic communication networks. However, only a few have tested such hypotheses experimentally and even fewer have investigated how directional signals affect receiver behavior. In this study, we measured directivity patterns of male northern elephant seal threat calls and used an acoustic playback approach to determine how call directionality influenced the responses of male seals in reproductive competition. We collected data on adult and older subadult seals on a breeding rookery (Ano Nuevo State Park) over three field seasons. Threat calls had substantial directionality, particularly at frequencies above 1 kHz and responses to playbacks depended on call directivity patterns. Males moved farther away from the playback source when it simulated a caller oriented toward them compared to when playbacks simulated a caller oriented away from them. These results suggest that threat call directionality provides meaningful information about the auditory scene and spatial orientation of male elephant seals in reproductive competition.

MALE ELEPHANT SEALS STAY STILL TO KEEP COOL

![Figure][1] The mating season is a time of great exertion for male elephant seals. Defending their harem, the males fast and lose approximately 36% of their body mass during their mating marathon. Not surprisingly, the well-insulated animals generate colossal amounts of heat during their

Long distance breeding dispersal of a southern elephant seal

Southern elephant seals range extensively during regular foraging excursions. Despite this they are highly philopatric and long range dispersal is rare. At Gough Island, southern Atlantic Ocean, we observed a breeding adult male elephant seal during September 2009, which had been tagged on its natal beach at Marion Island, southern Indian Ocean, in November 1998. The individual was resighted only once on Marion Island, 6 months after tagging. This 3,860 km movement represents dispersal (and likely gene flow) between distinct populations from different elephant seal geographical provinces. Given the polygynous breeding system of this species, the presence of this single male may have a disproportionate genetic effect on the small number of southern elephant seals breeding at Gough Island.

The Effect of Mating Motives on Risk Taking Likelihood Assessment in Men

According to sexual selection theory,intra-sex competition mainly among males leads to male characteristics known as weapons.The large body size and thick proboscis of male elephant seals and the robust horns and antlers of various ungulate stags are well-known examples of weapons.Inter-sex selection or mate choice,mostly exercised by the limiting sex or females,leads male characteristics known as ornaments.The vibrant colors of the guppy and the bright plumage of various birds are examples of ornaments.Whereas human males possess similar physical sex-dimorphic characteristics such as larger body frames (weapons),and lower voice pitch (ornaments),human sex-dimorphism is mainly shown as weapon-like (e.g.,aggression) and ornament-like behavior (e.g.,bragging).Human risk taking is such an ornament-like behavior because,like all ornaments which are functionally useless but are yet costly to sustain,risk taking behavior brings danger to its carriers without apparent functional purposes.Like ornaments,risk taking behavior is preferred by conspecific females who find its male carriers sexually attractive.The purpose of the present study was to test sexual selection theory on humans by investigating the association between risk-taking behavior and mating motives among men but not women.This hypothesis was tested against the rival hypothesis that risk taking may be externally motivated by monetary reward that renders similar effects on both men and women.These hypotheses were tested on a sample of 127 graduate students (62 males,mean age=21.47;SD= 1.59).In a between-group design,participants were exposed,on a computer screen,either to attractive opposite-sex pictures (the mating condition) or pictures of money or medals (the control or monetary reward condition).These two conditions were manipulated as a simple perceptual task where participants were instructed to decide on the location of each picture as it flashes on the screen (500 ms) by pressing one of two keys on the keyboard.This is to distract the participants from being aware of the intended experimental manipulation (mating versus monetary reward).To facilitate this distraction,attractive opposite sex pictures were also mixed with a small number of average-looking opposite sex pictures,and the monetary award pictures were mixed with a small number of non-reward scenes.After the picture exposure,each participant was given 19 different risk taking scenarios and was asked to assess the likelihood the participant would engage in each of the risk-taking behavior.The 19 risk-taking scenarios represent four domains of risk,including financial,health,social,and recreational risk.Composite scores representing the four domains were used as the dependent variables.Except for one of the four dependent variables,A 2 (mating vs.reward) × 2 (gender of the participants) ANOVA did not yield a significant interaction effect.However,separate t-tests were statistically significant,showing that men indicated higher likelihood to take risk after being exposed to attractive opposite-sex pictures than to reward pictures,whereas women did not show the difference in risk taking likelihood assessment besides social risk.Taking health risk for example,M=21.03 vs.18.67 under the mating vs.reward condition for men.The mean difference was statistically significant,p.01.For women,M=17.94 and 17.35,respectively.Other mean comparisons showed similar results which are reported in Table 1 in the main text.The results support sexual selection theory.Like most mammals,human males but not females have acquired ornament-like behaviors which are driven by mating motives.When attractive women are around,men are more likely to engage in functionally useless and potentially harmful behavior,which,however,are "useful" in the sense that they serve as signals of good genes.Thus,men's risk taking is driven by mating motives.Women are drawn to men's risk taking behavior for the same sexual selection reason,i.e.,women use the signals to select quality mates.In part to address reviewers' concerns,motives and need states serve as proximate cues that drive our behavior both consciously and unconsciously.In everyday life,mating motives,like many other motives,may remain unconscious most of the time which nonetheless drive and shape our behavior as is shown by the present study.

Click-evoked potentials in a large marine mammal, the adult male northern elephant seal (Mirounga angustirostris)

Auditory evoked potential (AEP) hearing studies in marine mammals should consider an expected size-dependent reduction in AEP amplitude. This study is the first to measure the click-evoked response in a large marine mammal, the adult male elephant seal (Mirounga angustirostris). Click stimuli were presented at peak-peak equivalent sound pressure levels of 117-118 dB re: 20 microPa. Three positive peaks (P1-P3) and two negative peaks (N4 and N5) were observed in the AEP. Response latencies were longer than previously observed in a 1.8 yr old seal and the maximum peak-peak amplitude was comparatively reduced by more than 60%. The inverse relationship between size and AEP amplitude will likely require increased averaging with larger subjects and possibly modifications to electrode placement and design in order to increase the quality of recorded evoked responses.

Development of aggressive vocalizations in male southern elephant seals (Mirounga leonina): maturation or learning?

Summary Vocalizations are an important component of male elephant seal agonistic behaviour. Acoustic and behavioural components of vocalizations emitted during agonistic contests show gross differences between young and old males, but the variation with age depends on the specific feature. Vocalizations become more frequent and effective at later ages. Acoustic features that are constrained by structural phenotype, which changes with age, also should change with age, while acoustic features that are independent from structural phenotype should show no relationship with age. We demonstrate that, in southern elephant seals, formant frequencies, which are constrained by the vocal tract length and, therefore, by body size, show a clear decrease with age, whereas temporal and structural features of sounds, which potentially are unconstrained, show no correlation with age. Formants ontogeny seems, therefore, to be mostly the result of body maturation, and hence formants may be reliable signals of age. In contrast, acoustic features such as temporal features and syllable structure, are free to change, and hence may serve as the raw material for vocal learning and individual recognition.

Locomotion in diving elephant seals: physical and physiological constraints

To better understand how elephant seals (Mirounga angustirostris) use negative buoyancy to reduce energy metabolism and prolong dive duration, we modelled the energetic cost of transit and deep foraging dives in an elephant seal. A numerical integration technique was used to model the effects of swim speed, descent and ascent angles, and modes of locomotion (i.e. stroking and gliding) on diving metabolic rate, aerobic dive limit, vertical displacement (maximum dive depth) and horizontal displacement (maximum horizontal distance along a straight line between the beginning and end locations of the dive) for aerobic transit and foraging dives. Realistic values of the various parameters were taken from previous experimental data. Our results indicate that there is little energetic advantage to transit dives with gliding descent compared with horizontal swimming beneath the surface. Other factors such as feeding and predator avoidance may favour diving to depth during migration. Gliding descent showed variable energy savings for foraging dives. Deep mid-water foraging dives showed the greatest energy savings (approx. 18%) as a result of gliding during descent. In contrast, flat-bottom foraging dives with horizontal swimming at a depth of 400m showed less of an energetic advantage with gliding descent, primarily because more of the dive involved stroking. Additional data are needed before the advantages of gliding descent can be fully understood for male and female elephant seals of different age and body composition. This type of data will require animal-borne instruments that can record the behaviour, three-dimensional movements and locomotory performance of free-ranging animals at depth.

Having a big nose: structure, ontogeny, and function of the elephant seal proboscis

The proboscis of male elephant seals ( Mirounga Gray, 1827) has been suggested as an example of a secondary sexual trait since Darwin. There has been much speculation about its social function (e.g., optical signal of breeding status, amplification of vocalizations, cue for female choice). However, it has never been studied in detail, probably because its fleshy nature makes measurement difficult. In this paper, we employ photogrammetry to measure the proboscis and facial morphology of a large sample of wild, unrestrained, displaying male southern elephant seals ( Mirounga leonina (L., 1758)). We describe ontogeny and allometry of the proboscis and analyze current phenotypic selection pressures on proboscis traits. We discuss the potential role of the proboscis in optical and acoustic signaling of male resource-holding potential and status. We demonstrate that proboscis size is positively correlated with age and body size independently, and that it is currently under a positive sexual selection pressure when the effect of selection on body size is removed. We suggest that selection on proboscis size is functionally related to the emission of agonistic vocalizations.

Click and tone-pip auditory evoked potentials in a large marine mammal, the northern elephant seal

The use of auditory-evoked potentials (AEPs) to study the hearing of mysticete whales is challenged by access to animals, their large size, and proportionately smaller brain relative to odontocetes. One means by which AEP techniques can be adapted to these larger animals is by application to more readily available proxy species. The northern elephant seal (Mirounga angustirostris) is a large pinniped, potentially in excess of 2000 kg, with a thick dermis, large skull, relatively small auditory nerve, and a low-frequency vocal communication system. AEP collection in elephant seals provides similar challenges to those of the mysticetes but at a scale that provides a greater opportunity for success. AEP tests were conducted on northern elephant seals at Año Nuevo State Reserve, the natural haul-out site of the elephant seal. Subjects were chemically immobilized with tiletamine/zolazepam and chemical restraint was maintained with bolus injections of ketamine. Click-evoked potentials were collected from four weanling and two adult male elephant seals and tone-pip-evoked potentials were collected from a 2-year-old female. Results demonstrate that AEPs can be recorded from large pinniped species, providing a step towards the application of similar techniques to larger cetacean species.