Population density shapes patterns of survival and reproduction in Eleutheria dichotoma (Hydrozoa: Anthoathecata)

Schaible

2019

Estuaries and Coasts

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Salinity conditions experienced by organisms in coastal regions may shape their life histories. Here, salinity's impact on reproduction and survival of the hydrozoan Eleutheria dichotoma was investigated using laboratory-cultured individuals originating from Banyuls-sur-Mer (southern France) collected several decades ago. During the experiment (October 2014-July 2015), hydroid colonies and medusae were exposed to three salinities (25, 35, 45). Asexually budded medusae were collected from colonies and reared for three generations obtained by asexual budding of medusae. Salinities experienced by hydroid colonies had only minor effects on initial size, time to maturity, medusa budding, sexual production of planulae by medusae, and survival. In contrast, salinities experienced by medusae influenced their life histories. Compared with medium salinity (35), lowsalinity medusae (25) had an earlier onset and higher rates of asexual budding, a later onset and slower rates of sexual reproduction, and higher mortality, which could result from allocation tradeoffs. The increased production of planulae by medusae in low salinity indicated that they were transitioning to a benthic polyp life form more resistant to environmental stress. High salinity (45) delayed asexual maturity, prevented sexual maturity in medusae, and led to lower survival and asexual reproduction rates. Budding rates decreased across the generations; however, planula production rates decreased in medium salinity but increased in low salinity. This might be explained by the accumulation of damage with each generation, and/or by internal rhythms. The flexible responses of this tractable model organism, Eleutheria dichotoma, to salinity change may be useful in future studies on changing estuarine conditions.

Section: Culture Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Salinity Effects on Survival and Reproduction of Hydrozoan Eleutheria dichotoma

Schaible

2019

Estuaries and Coasts

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“…Unfortunately, the usefulness of these concepts was corrupted by the association with specific sets of life history traits. This corruption was started unintentionally by Pianka ( 1970 ), who correctly enumerated traits of r -selected species, such as rapid development, early reproduction, and small size, as traits that lead to high r in Euler–Lotka equation (see also Kozłowski 2006 ; Dańko et al 2018 ). Unfortunately, he assigned the opposite traits to K -selected species.…”

Section: Introductionmentioning

confidence: 99%

Extrinsic Mortality Can Shape Life-History Traits, Including Senescence

et al. 2018

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The Williams’ hypothesis is one of the most widely known ideas in life history evolution. It states that higher adult mortality should lead to faster and/or earlier senescence. Theoretically derived gradients, however, do not support this prediction. Increased awareness of this fact has caused a crisis of misinformation among theorists and empirical ecologists. We resolve this crisis by outlining key issues in the measurement of fitness, assumptions of density dependence, and their effect on extrinsic mortality. The classic gradients apply only to a narrow range of ecological contexts where density-dependence is either absent or present but with unrealistic stipulations. Re-deriving the classic gradients, using a more appropriate measure of fitness and incorporating density, shows that broad ecological contexts exist where Williams’ hypothesis is supported.Electronic supplementary materialThe online version of this article (10.1007/s11692-018-9458-7) contains supplementary material, which is available to authorized users.

“…Fertile specimens are more frequent shallower than 1,000 m (Figure 6f), indicating constraints not only on size in the deep sea but also on sexual reproduction, possibly due to lower population densities in the deep sea. Sexual reproduction has been reported to be less frequent in lower population densities for one well-studied species of hydroid (Danko, Schaible, Pijanowska & Danko, 2018). The pattern may be evidence that deep-sea hydroid populations are functioning under source-sink dynamics, in which the deep sea would function as a sink for some shallower water species, and where low nutrient input and low population densities would not sustain reproductive populations immigrating from shallower sources (Rex et al, 2005).…”

Section: Discussionmentioning

confidence: 99%

Traits and depth: What do hydroids tell us about morphology and life‐history strategies in the deep sea?

Fernandez

Collins

Gittenberger

et al. 2020

Global Ecol Biogeogr

Aim Traits affect the survival and reproduction of individuals in different habitat conditions, ultimately altering their distributions. In the oceans, changes in environmental conditions with bathymetry may influence the occurrence of specific traits. Therefore, characterizing trait variation with depth can illuminate drivers related to the distribution of diversity of forms, functions, and life histories. We aimed to investigate patterns of variation in the diversified life histories and morphologies of hydroids with depth, integrating these patterns with the natural history of the group and ecological principles of the deep sea. Location Atlantic Ocean and adjacent polar seas, from 50 to 5,330 m deep. Time period Present day. Major taxa studied Hydrozoa. Methods Analyses were based on 14 traits collected for a total of 4,668 specimens of hydroids, belonging to 438 species. Records were divided into 12 depth strata for comparisons. We evaluated: how each trait varies with depth; whether variation in some traits is affected by the presence of other traits; how traits covary; and similarities in trait compositions among depth strata. Results Traits of hydroids vary with depth, with more pronounced differences for regions deeper than 1,000 m. Hydroids are generally smaller, infertile, solitary, meroplanktonic, and devoid of protective structures with increasing depth. The relationship, however, is not always linear. Also, some covariation and correlation between traits was evident. For example, depth may affect size differently according to the presence of specific traits such as structures protecting against predation. The lower proportion of fertile specimens recorded in the deep sea suggests that chances for genetic recombination are reduced in deep‐sea populations, ultimately leading to a slower rate of evolution. Main conclusions We identified novel trends in hydroid trait variation with depth by combining observations on morphology, ecology, and life history, clarifying selection pressures on hydroids in the deep sea.