79 research outputs found
Estimating maturity from size-at-age data: are real-world fisheries datasets up to the task?
The size and age at which individuals mature is rapidly changing due to plastic and evolved responses to fisheries harvest and global warming. Understanding the nature of these changes is essential because maturity schedules are critical in determining population demography and ultimately, the economic value and viability of fisheries. Detecting maturity changes is, however, practically difficult and costly. A recently proposed biphasic growth modelling likelihood profiling method offers great potential as it can statistically estimate age-at-maturity from population-level size-at-age data, using the change-point in growth that occurs at maturity. Yet, the performance of the method on typical marine fisheries datasets remains untested. Here, we assessed the suitability of 12 North Sea and Australian species’ datasets for the likelihood profiling approach. The majority of the fisheries datasets were unsuitable as they had too small sample sizes or too large size-at-age variation. Further, datasets that did satisfy data requirements generally showed no correlation between empirical and model-derived maturity estimates. To understand why the biphasic approach had low performance we explored its sensitivity using simulated datasets. We found that method performance for marine fisheries datasets is likely to be low because of: (1) truncated age structures due to intensive fishing, (2) an under-representation of young individuals in datasets due to common fisheries-sampling protocols, and (3) large intrapopulation variability in growth curves. To improve our ability to detect maturation changes from population level size-at-age data we need to improve data collection protocols for fisheries monitoring
Smaller adult fish size in warmer water is not explained by elevated metabolism
Fish and other ectotherms living in warmer waters often grow faster as juveniles, mature earlier, but become smaller adults. Known as the temperature-size rule (TSR), this pattern is commonly attributed to higher metabolism in warmer waters, leaving fewer resources for growth. An alternative explanation focuses on growth and reproduction trade-offs across temperatures. We tested these hypotheses by measuring growth, maturation, metabolism and reproductive allocation from zebrafish populations kept at 26 and 30°C across six generations. Zebrafish growth and maturation followed TSR expectations but were not explained by baseline metabolic rate, which converged between temperature treatments after a few generations. Rather, we found that females at 30°C allocated more to reproduction, especially when maturing at the smallest sizes. We show that elevated temperatures do not necessarily increase baseline metabolism if sufficient acclimation is allowed and call for an urgent revision of modelling assumptions used to predict population and ecosystem responses to warming
Is oxygen limitation in warming waters a valid mechanism to explain decreased body sizes in aquatic ectotherms?
Aim:The negative correlation between temperature and body size of ectothermic animals (broadly known as the temperature‐size rule or TSR) is a widely observed pattern, especially in aquatic organisms. Studies have claimed that the TSR arises due to decreased oxygen solubility and increasing metabolic costs at warmer temperatures, whereby oxygen supply to a large body becomes increasingly difficult. However, mixed empirical evidence has led to a controversy about the mechanisms affecting species’ size and performance under different temperatures. We review the main competing genetic, physiological and ecological explanations for the TSR and suggest a roadmap to move the field forward.
Location: Global.
Taxa: Aquatic ectotherms.
Time period: 1980–present.
Results: We show that current studies cannot discriminate among alternative hypotheses and none of the hypotheses can explain all TSR‐related observations. To resolve this impasse, we need experiments and field‐sampling programmes that specifically compare alternative mechanisms and formally consider energetics related to growth costs, oxygen supply and behaviour. We highlight the distinction between evolutionary and plastic mechanisms, and suggest that the oxygen limitation debate should separate processes operating on short, decadal and millennial time‐scales.
Conclusions: Despite decades of research, we remain uncertain whether the TSR is an adaptive response to temperature‐related physiological (enzyme activity) or ecological changes (food, predation and other mortality), or a response to constraints operating at a cellular level (oxygen supply and associated costs). To make progress, ecologists, physiologists, modellers and geneticists should work together to develop a cross‐disciplinary research programme that integrates theory and data, explores time‐scales over which the TSR operates, and assesses limits to adaptation or plasticity. We identify four questions for such a programme. Answering these questions is crucial given the widespread impacts of climate change and reliance of management on models that are highly dependent on accurate representation of ecological and physiological responses to temperature
Cuticular Compounds Bring New Insight in the Post-Glacial Recolonization of a Pyrenean Area: Deutonura deficiens Deharveng, 1979 Complex, a Case Study
Background: In most Arthropod groups, the study of systematics and evolution rely mostly on neutral characters, in this context cuticular compounds, as non-neutral characters, represent an underexplored but potentially informative type of characters at the infraspecific level as they have been routinely proven to be involved in sexual attraction. Methods and Findings: The collembolan species complex Deutonura deficiens was chosen as a model in order to test the utility of these characters for delineating four infraspecific entities of this group. Specimens were collected for three subspecies (D. d. deficiens, D. d. meridionalis, D. d. sylvatica) and two morphotypes (D. d. sylvatica morphoype A and B) of the complex; an additional species D. monticola was added. Cuticular compounds were extracted and separated by gas chromatography for each individual. Our results demonstrate that cuticular compounds succeeded in separating the different elements of this complex. Those data allowed also the reconstruction of the phylogenetic relationships among them. Conclusions: The discriminating power of cuticular compounds is directly related to their involvement in sexual attraction and mate recognition. These findings allowed a discussion on the potential involvement of intrinsic and paleoclimatic factors in the origin and the diversification of this complex in the Pyrenean zone. This character type brings the first advanc
Out of Their Depth? Isolated Deep Populations of the Cosmopolitan Coral Desmophyllum dianthus May Be Highly Vulnerable to Environmental Change
Deep sea scleractinian corals will be particularly vulnerable to the effects of
climate change, facing loss of up to 70% of their habitat as the
Aragonite Saturation Horizon (below which corals are unable to form calcium
carbonate skeletons) rises. Persistence of deep sea scleractinian corals will
therefore rely on the ability of larvae to disperse to, and colonise, suitable
shallow-water habitat. We used DNA sequence data of the internal transcribed
spacer (ITS), the mitochondrial ribosomal subunit (16S) and mitochondrial
control region (MtC) to determine levels of gene flow both within and among
populations of the deep sea coral Desmophyllum dianthus in SE
Australia, New Zealand and Chile to assess the ability of corals to disperse
into different regions and habitats. We found significant genetic subdivision
among the three widely separated geographic regions consistent with isolation
and limited contemporary gene flow. Furthermore, corals from different depth
strata (shallow <600 m, mid 1000–1500 m, deep >1500 m) even on the
same or nearby seamounts were strongly differentiated, indicating limited
vertical larval dispersal. Genetic differentiation with depth is consistent with
the stratification of the Subantarctic Mode Water, Antarctic Intermediate Water,
the Circumpolar Deep and North Pacific Deep Waters in the Southern Ocean, and we
propose that coral larvae will be retained within, and rarely migrate among,
these water masses. The apparent absence of vertical larval dispersal suggests
deep populations of D. dianthus are unlikely to colonise
shallow water as the aragonite saturation horizon rises and deep waters become
uninhabitable. Similarly, assumptions that deep populations will act as refuges
for shallow populations that are impacted by activities such as fishing or
mining are also unlikely to hold true. Clearly future environmental management
strategies must consider both regional and depth-related isolation of deep-sea
coral populations
Mysid crustaceans as standard models for the screening and testing of endocrine-disrupting chemicals
Author Posting. © Springer, 2007. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Ecotoxicology 16 (2007): 205-219, doi:10.1007/s10646-006-0122-0.Investigative efforts into the potential endocrine-disrupting effects of chemicals have mainly
concentrated on vertebrates, with significantly less attention paid to understanding potential
endocrine disruption in the invertebrates. Given that invertebrates account for at least 95% of all
known animal species and are critical to ecosystem structure and function, it remains essential to
close this gap in knowledge and research. The lack of progress regarding endocrine disruption in
invertebrates is still largely due to: (1) our ignorance of mode-of-action, physiological control, and
hormone structure and function in invertebrates; (2) lack of a standardized invertebrate assay; (3)
the irrelevance to most invertebrates of the proposed activity-based biological indicators for
endocrine disruptor exposure (androgen, estrogen and thyroid); (4) limited field studies. Past and
ongoing research efforts using the standard invertebrate toxicity test model, the mysid shrimp, have
aimed at addressing some of these issues. The present review serves as an update to a previous
publication on the use of mysid shrimp for the evaluation of endocrine disruptors (Verslycke et al.,
2004a). It summarizes recent investigative efforts that have significantly advanced our
understanding of invertebrate-specific endocrine toxicity, population modeling, field studies, and
transgeneration standard test development using the mysid model.Supported by a Fellowship of the Belgian American Educational Foundation
Effects of fishery protection on biometry and genetic structure of two target sea cucumber species from the Mediterranean Sea
Sea cucumber fisheries are now occurring
in most of the tropical areas of the world, having
expanded from its origin in the central Indo-Pacific.
Due to the overexploitation of these resources and the
increasing demand from Asian countries, new target
species from Mediterranean Sea and northeastern
Atlantic Ocean are being caught. The fishery effects
on biometry and genetic structure of two target species
(Holothuria polii and H. tubulosa) from Turkey, were
assessed. The heaviest and largest individuals of H.
polii were found into the non-fishery area of Kusadasi,
also showing the highest genetic diversity. Similar
pattern was detected in H. tubulosa, but only the
weight was significantly higher in the protected area.
However, the observed differences on the fishery
effects between species, could be explained considering
the different percentage of catches (80% for H.
polii and 20% for H. tubulosa)
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