Spring mortality of the cyclopoid copepod Oithona similis in polar waters

Hirst, Andrew G.; Ward, Peter

doi:10.3354/meps07694

Cited by 19 publications

(20 citation statements)

References 28 publications

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“…Based on VLT mortality methods, C. helgolandicus CV‐male total mortality rates were ∼ 2.5 times greater than CV‐female rates; a phenomenon that has been reported with other copepod species. For example, Oithona similis male mortality rates were estimated to be ∼ 12 times those of females in polar waters (Hirst and Ward ), and Calanus pacificus male mortality rates were 2–3 times higher than female rates in California (Ohman and Hsieh ).…”

Section: Discussionmentioning

confidence: 99%

Mortality of Calanus helgolandicus: Sources, differences between the sexes and consumptive and nonconsumptive processes

Maud

Hirst

Atkinson

et al. 2018

Limnology & Oceanography

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While losses from mortality are as important as gains from reproduction in zooplankton population dynamics, the former are more challenging to quantify. We used two approaches to provide complementary insights into the mortality of a biomass-dominant copepod, Calanus helgolandicus, at Station L4 in the English Channel. Using a neutral-red staining method, we found that dead carcasses represented a mean of 9% of the C. helgolandicus copepodites sampled. The resulting nonconsumptive mortality rates are the first that have been derived for C. helgolandicus; and estimates suggest a contribution of 0-54% (median of 4.4%) to the total mortality rate. Consumptive mortality (i.e., that due to removal by predation), dominated for most of the year and contributed a mean of 89% to total mortality. Nonconsumptive mortality increased during summer and winter, and was positively related to maximum wind speed during the preceding 72 h, indicating that extreme weather events may lead to increased mortality. Using the Vertical Life Table approach, mortality rates across the CV-adult male stage pair were on average 2.5 times greater than those of CV-adult females. Adult male consumptive mortality rates were 6 times greater than those for females; adult male nonconsumptive rates were twice those of females, suggesting that predation is of greater significance to male loss rates. Summer CV-adult mortality rates were positively correlated to temperature, and to the abundance of predatory chaetognaths and siphonophores, suggesting that the gelatinous predator assemblage is the dominant agent for population control of late stage copepodites of C. helgolandicus at L4.

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Section: Discussionmentioning

confidence: 99%

Mortality of Calanus helgolandicus: Sources, differences between the sexes and consumptive and nonconsumptive processes

Maud

Hirst

Atkinson

et al. 2018

Limnology & Oceanography

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“…The sedentary versus roving dichotomy [1] is partly equivalent to ambush feeding cyclopoid copepods, such as in the genus Oithona: in this example, the female is an ambush feeder and relatively non-motile, whereas the males spend approximately one-third of their time swimming at high speed in search for females [35]. As a result, the males have much higher mortality, and adult sex ratios are strongly female-biased, typically with a male to female ratio of 1 : 10 [15,36]. However, time-out ratios are strongly female-biased because the females need to be mated only once, whereas the males can mate several times per day, and OSR is likely less skewed than the sex ratio would suggest (figure 4).…”

Section: (I) Free-living Copepodsmentioning

confidence: 99%

Macroevolutionary patterns of sexual size dimorphism in copepods

Hirst

Kiørboe

2014

Proc. R. Soc. B.

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Major theories compete to explain the macroevolutionary trends observed in sexual size dimorphism (SSD) in animals. Quantitative genetic theory suggests that the sex under historically stronger directional selection will exhibit greater interspecific variance in size, with covariation between allometric slopes (male to female size) and the strength of SSD across clades. Rensch's rule (RR) also suggests a correlation, but one in which males are always the more size variant sex. Examining free-living pelagic and parasitic Copepoda, we test these competing predictions. Females are commonly the larger sex in copepod species. Comparing clades that vary by four orders of magnitude in their degree of dimorphism, we show that isometry is widespread. As such we find no support for either RR or for covariation between allometry and SSD. Our results suggest that selection on both sexes has been equally important. We next test the prediction that variation in the degree of SSD is related to the adult sex ratio. As males become relatively less abundant, it has been hypothesized that this will lead to a reduction in both inter-male competition and male size. However, the lack of such a correlation across diverse free-living pelagic families of copepods provides no support for this hypothesis. By comparison, in sea lice of the family Caligidae, there is some qualitative support of the hypothesis, males may suffer elevated mortality when they leave the host and rove for sedentary females, and their femalebiased SSD is greater than in many free-living families. However, other parasitic copepods which do not appear to have obvious differences in sex-based mate searching risks also show similar or even more extreme SSD, therefore suggesting other factors can drive the observed extremes.

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“…Planktonic copepods may, however, be good model organisms to experimentally test the predictions of the evolutionary theory of ageing. There are two principal feeding modes in planktonic copepods: they can be passive ambush feeders, or they can be active predators that cruise through the water or generate a feeding current (Green 1986, Kiørboe 2011, with the active mode leading to a much higher predation risk (Kiørboe et al 2010b) and higher mortality rates in the field (Eiane andOhman 2004, Hirst andWard 2008). Different species have very different feeding and matefinding behaviors that expose them differently to predation risk (Kiørboe 2008), and they have different degrees of parental care (Mauchline 1998), which leads to predicted differences in average life span, ageing, and fecundity rates.…”

Section: Introductionmentioning

confidence: 99%

Interrelations between senescence, life‐history traits, and behavior in planktonic copepods

Kiørboe

Ceballos

Thygesen

2015

Ecology

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The optimal allocation of resources to repair vs. reproduction in an organism may depend on the magnitude and pattern of the external mortality it is experiencing, which, in turn, may depend on its feeding and mate-finding behavior. Thus, the fundamental activities of an organism, i.e., to feed, to survive, and to reproduce, are interrelated through trade-offs. Here, we use small planktonic copepods to examine how adult longevity and ageing patterns in a protected laboratory environment relate to the feeding mode (active searching vs. passive ambush feeding), mate-finding behavior, and spawning mode of the species. We show that average adult longevity varies between species by an order of magnitude and is independent of body size. Ambush feeders that carry their eggs have longer average life spans and experience higher mortality later in life relative to active feeders that broadcast their eggs. Males generally have shorter life spans and experience higher mortality earlier in life than females, and this difference may be accentuated in species where dangerous mate-finding is male biased. We finally show a trade-off between longevity and fecundity, with ambush feeders producing eggs at a rate five to 10 times lower than the active feeders, consistent with predictions from optimal resource allocation theory.

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Spring mortality of the cyclopoid copepod Oithona similis in polar waters

Cited by 19 publications

References 28 publications

Mortality of Calanus helgolandicus: Sources, differences between the sexes and consumptive and nonconsumptive processes

Mortality of Calanus helgolandicus: Sources, differences between the sexes and consumptive and nonconsumptive processes

Macroevolutionary patterns of sexual size dimorphism in copepods

Interrelations between senescence, life‐history traits, and behavior in planktonic copepods

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