The high cost of reproduction in sea otters necessitates unique physiological adaptations

Thometz, Nicole M.; Kendall, Traci; Richter, Beau; Williams, Terrie M.

doi:10.1242/jeb.138891

Cited by 23 publications

(17 citation statements)

References 46 publications

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“…Most mustelids exhibit elongate body plans 72 and therefore increased energy requirements imposed by an increased surface-to-volume ratio 73–75 . Rearing of young further increases these energetic demands; for example, lactating southern sea otters ( Enhydra lutris neresis ) exhibit daily energy demands 85–110% higher than non-reproductive females 76,77 . Therefore, selection for smaller female body sizes would theoretically reduce the absolute food requirements needed to rear young 51,63,70,71 .…”

Section: Discussionmentioning

confidence: 99%

Solitary meat-eaters: solitary, carnivorous carnivorans exhibit the highest degree of sexual size dimorphism

Law

2019

Sci Rep

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Although sexual size dimorphism (SSD) is widespread across the animal tree of life, the underlying evolutionary processes that influence this phenomenon remains elusive and difficult to tease apart. In this study, I examined how social system (as a proxy for sexual selection) and diet (as a proxy for natural selection) influenced the evolution of SSD in terrestrial carnivorans (Carnivora; Mammalia). Using phylogenetic comparative methods, I found that are territorial solitary and carnivorous carnivorans exhibited selection towards increased degree of male-biased SSD compared to other carnivorans with alternative social systems and diets. I also found the absence of Rensch’s rule across most carnivoran clades, suggestion a relaxation of the influences of sexual selection on SSD. These results together suggest that sexual selection and niche divergence together are important processes influencing the evolution of male-biased SSD in extant terrestrial carnivorans.

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Section: Discussionmentioning

confidence: 99%

Solitary meat-eaters: solitary, carnivorous carnivorans exhibit the highest degree of sexual size dimorphism

Law

2019

Sci Rep

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“…Female mammals with k‐selected traits make huge energy investments in reproduction and parental care to ensure survival of offspring (most marine mammals produce a single offspring every 1–3 years; Berta, Sumich, & Kovacs, ). For some marine mammals, for example, sea otters, lactation can be a significant physiological drain on energetic reserves (Thometz, Kendall, Richter, & Williams, ). The energetic deficits could potentially be intensified by additional man‐made (ocean noise) or natural stressors (e.g., predators).…”

Section: Discussionmentioning

confidence: 99%

To feed or not to feed? Bioenergetic impacts of fear‐driven behaviors in lactating dolphins

Srinivasan

Swannack

Grant³

et al. 2017

Ecology and Evolution

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In mammals, lactation can be the most energetically expensive part of the reproductive cycle. Thus, when energy needs are compromised due to predation risk, environmental disturbance, or resource scarcity, future reproductive success can be impacted. In marine and terrestrial environments, foraging behavior is inextricably linked to predation risk. But quantification of foraging energetics for lactating animals under predation risk is less understood. In this study, we used a spatially explicit individual‐based model to study how changes in physiology (lactating or not) and the environment (predation risk) affect optimal behavior in dolphins. Specifically, we predicted that an adult dolphin without calf would incur lower relative energetic costs compared to a lactating dolphin with calf regardless of predation risk severity, antipredator behavior, or prey quality consumed. Under this state‐dependent analysis of risk approach, we found predation risk to be a stronger driver in affecting total energetic costs (foraging plus locomotor costs) than food quality for both dolphin types. Further, contrary to our hypothesis, after accounting for raised energy demands, a lactating dolphin with calf does not necessarily have higher relative‐to‐baseline costs than a dolphin without calf. Our results indicate that both a lactating (with calf) and non‐lactating dolphin incur lowered energetic costs under a risk‐averse behavioral scheme, but consequently suffer from lost foraging calories. A lactating dolphin with calf could be particularly worse off in lost foraging calories under elevated predation risk, heightened vigilance, and increased hiding time relative to an adult dolphin without calf. Further, hiding time in refuge could be more consequential than detection distance for both dolphin types in estimated costs and losses incurred. In conclusion, our study found that reproductive status is an important consideration in analyzing risk effects in mammals, especially in animals with lengthy lactation periods and those exposed to both biological and nonbiological stressors.

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“…In order to survive, animals must remain in positive energy balance over their lifetime, with energy acquisition occurring via food, and energy expenditure occurring via movement ( Nathan et al, 2008 ; Shepard et al, 2013 ), growth (including tissue regeneration) ( Careau et al, 2013 ; Pontzer et al, 2014 ), reproduction ( Gittleman & Thompson, 1988 ; Thometz et al, 2016 ), and physiological homeostasis ( Haim & Borut, 1981 ; Silva, 2005 ). Temperature regulation has been subject to particular interest within the scientific community because variations in environmental temperature are clear stressors that can be measurable.…”

Section: Introductionmentioning

confidence: 99%

The metabolic response of theBradypussloth to temperature

Cliffe

Scantlebury

Kennedy

et al. 2018

PeerJ

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Poikilotherms and homeotherms have different, well-defined metabolic responses to ambient temperature (Ta), but both groups have high power costs at high temperatures. Sloths (Bradypus) are critically limited by rates of energy acquisition and it has previously been suggested that their unusual departure from homeothermy mitigates the associated costs. No studies, however, have examined how sloth body temperature and metabolic rate vary with Ta. Here we measured the oxygen consumption (VO2) of eight brown-throated sloths (B. variegatus) at variable Ta’s and found that VO2 indeed varied in an unusual manner with what appeared to be a reversal of the standard homeotherm pattern. Sloth VO2 increased with Ta, peaking in a metabolic plateau (nominal ‘thermally-active zone’ (TAZ)) before decreasing again at higher Ta values. We suggest that this pattern enables sloths to minimise energy expenditure over a wide range of conditions, which is likely to be crucial for survival in an animal that operates under severe energetic constraints. To our knowledge, this is the first evidence of a mammal provisionally invoking metabolic depression in response to increasing Ta’s, without entering into a state of torpor, aestivation or hibernation.

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The high cost of reproduction in sea otters necessitates unique physiological adaptations

Cited by 23 publications

References 46 publications

Solitary meat-eaters: solitary, carnivorous carnivorans exhibit the highest degree of sexual size dimorphism

Solitary meat-eaters: solitary, carnivorous carnivorans exhibit the highest degree of sexual size dimorphism

To feed or not to feed? Bioenergetic impacts of fear‐driven behaviors in lactating dolphins

The metabolic response of theBradypussloth to temperature

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