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Differences in Time until Dispersal between Cryptic Species of a Marine Nematode Species Complex

DOI:10.1371/journal.pone.0042674
Authors:
Nele De Meester at Ghent University
Nele De Meester
Sofie Derycke at Institute for agriculture and fisheries (ILVO)
Sofie Derycke
  • Institute for agriculture and fisheries (ILVO)
Tom Moens at Ghent University
Tom Moens
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Co-occurrence of closely related species may be achieved in environments with fluctuating dynamics, where competitively inferior species can avoid competition through dispersal. Here we present an experiment in which we compared active dispersal abilities (time until first dispersal, number and gender of dispersive adults, and nematode densities at time of dispersal) in Litoditis marina, a common bacterivorous nematode species complex comprising four often co-occurring cryptic species, Pm I, II, III, and IV, as a function of salinity and food distribution. The experiment was conducted in microcosms consisting of an inoculation plate, connection tube, and dispersal plate. Results show species-specific dispersal abilities with Pm I dispersing almost one week later than Pm III. The number of dispersive adults at time of first dispersal was species-specific, with one dispersive female in Pm I and Pm III and a higher, gender-balanced, number in Pm II and Pm IV. Food distribution affected dispersal: in absence of food in the inoculation plate, all species dispersed after ca four days. When food was available Pm I dispersed later, and at the same time and densities irrespective of food conditions in the dispersal plate (food vs no food), suggesting density-dependent dispersal. Pm III dispersed faster and at a lower population density. Salinity affected dispersal, with slower dispersal at higher salinity. These results suggest that active dispersal in Litoditis marina is common, density-dependent, and with species, gender- and environment-specific dispersal abilities. These differences can lead to differential responses under suboptimal conditions and may help to explain temporary coexistence at local scales.
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... Litoditis marina is a bacterial-feeding cryptic nematode species complex associated with living and decomposing macroalgae in intertidal zones, and consists of species that often co-occur at local scales (Derycke et al., 2006. These co-occurring species have partly different ecological and functional traits (De Meester et al., 2011, De Meester et al., 2012De Meester et al., 2015a, b, De Meester et al., 2016, exhibit subtle differences in microhabitat preferences (Guden et al., 2018), and respond differently to gradients of resource diversity (Guden et al., 2021), indicating niche differentiation between cryptic species. In addition, intraspecific competition is prominent in L. marina (De Meester et al., 2015a), with pronounced intraspecific microbiome variability thatamong other thingsmay indicate individual dietary specialization (Derycke et al., 2016;Vafeiadou et al., 2022). ...
... Minimum juvenile development time, total fecundity, and adult population growth (total number of adults over time), which all contribute to population fitness (Moens and Vincx, 2000a), were quantified daily for a period of 7 days, corresponding to at least one and at most two generations in all species and food-diversity treatments (De Meester et al., 2015b). Minimum juvenile development time was defined as the time from the occurrence of the first juveniles until the appearance of the first F1-adult(s), which was used instead of minimum development time to take into account the differences in reproductive strategies between cryptic species (De Meester et al., 2012). In addition, the sum of the numbers of eggs and juveniles produced from the start of the incubation to the maturation of the first F1-offspring to adults was divided by the number of inoculated adult females (5 for 'low nematode density', 20 for 'high nematode density') to obtain an estimate of total fecundity per female (Moens and Vincx, 2000a). ...
... In this respect, intraspecific variation is expected to break down competitive hierarchies, making competitive exclusion less likely or less rapid (Hubbell, 2006;Fridley et al., 2007). While the different cryptic species of L. marina exhibit ecological-and functional-trait differences (De Meester et al., 2011, De Meester et al., 2012De Meester et al., 2015a, b, De Meester et al., 2016Guden et al., 2018, Guden et al., 2021, which provide support for niche differentiation as a driver of species coexistence, a competitive intransitive network (i.e., non-hierarchical competition) likely exists in L. marina (De Meester, 2016). Such competitive intransitivity indicates that there is no single best competitor, which can slow down the process of competitive exclusion and make neutral processes more important Schamp, 2006, 2008;Soliveres and Allan, 2018). ...
Resource diversity mitigates the effects of intraspecific competition in co-occurring cryptic nematode species
Article
Full-text available
  • Apr 2024
Intraspecific competition and resource diversity are considered major drivers of niche differentiation, which are expected to promote population niche expansion by driving individuals to feed on alternative resources and/or by enhancing individual diet specialization. Nevertheless, experimental studies on the interaction effects of both factors on animal behavior and population dynamics remain scant. Here, we investigate how resource diversity alters the impact of intraspecific competition on resource preference and fitness of three co-occurring cryptic species of the marine nematode complex Litoditis marina (Pm I, Pm III and Pm IV). For each cryptic species, two competition regimes (‘low nematode density’ and ‘high nematode density’) were established in microcosms with varying resource diversity ( E. coli , low-, medium- and high-diversity food). Our results show differences in resource preference and population fitness depending on intraspecific competition and resource diversity, but the response also varied considerably between cryptic species. Pm III did not exhibit resource preference under low intraspecific competition, but preferred the two most diverse food sources under high intraspecific competition. Pm IV also showed preference for medium-diversity food under high competition, whereas no resource preference was observed in Pm I regardless of competition regimes and resource diversity. Nevertheless, all cryptic species exhibited enhanced adult population growth on a more diverse food source under stronger intraspecific competition. These results indicate that resource diversity can alleviate intraspecific competition and affect niche diversification, which may impact diversity maintenance in ecological communities.
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... For example, while a low level of suitable food increases the frequency and extent of emigration, sufficient food supplies can have the opposite effect even at higher population densities (e.g. 11,12,[15][16][17][18]. A sufficient food supply can be a prerequisite for effective dispersal because well-fed, healthy individuals who have completed their physical development will be more likely to emigrate and will better survive the transfer than their malnourished and underdeveloped counterparts 19-21 . ...
... Thus, in this study C. elegans served as the model organism to investigate the effects of organismal density, food availability, and the presence of a predator, both individually and in combination, as triggers of emigration. Our experiments were conducted in two-patch systems, similar to the method employed by Fronhofer et al. 26 in unicellular organisms and metazoans, such as crustaceans, mollusks, arthopods, and vertebrates, and successfully adapted to nematodes by Meester et al. 10,16 . ...
... All experiments were performed in testing arenas consisting of two round chambers (Ø 5 cm) made from 1.3-cm plexiglass and connected by a 10-cm-long corridor (1 cm in width) that had been milled to a depth of 1 cm (Fig. 1). These dimensions were determined in previous nematode migration studies 10,16,36 and are based on the actual velocity (crawling or swimming) of different nematode species. For example, C. elegans is able to move up to 15 mm per minute 36 . ...
Population density, bottom-up and top-down control as an interactive triplet to trigger dispersal
Article
Full-text available
  • Apr 2022
Dispersal reflects the trade-offs between the cost of a change in habitat and the fitness benefits conferred by that change. Many factors trigger the dispersal of animals, but in field studies they are typically not controllable; consequently, they are mostly studied in the laboratory, where their single and interactive effects on dispersal can be investigated. We tested whether three fundamental factors, population density as well as bottom-up and top-down control, influence the emigration of the nematode Caenorhabditis elegans . Nematode movement was observed in experiments conducted in two-chamber arenas in which these factors were manipulated. The results showed that both decreasing food availability and increasing population density had a positive influence on nematode dispersal. The presence of the predatory flatworm Polycelis tenuis did not consistently affect dispersal but worked as an amplifier when linked with population density with respect to certain food-supply levels. Our study indicates that nematode dispersal on small scales is non-random; rather, the worms’ ability to perceive environmental information leads to a context-dependent decision by individuals to leave or stay in a patch. The further use of nematodes to gain insights into both the triggers that initiate dispersal, and the traits of dispersing individuals will improve the modeling of animal behavior in changing and spatial heterogenous landscapes.
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... This species complex is composed of cryptic species that often co-occur in the field (Derycke et al., 2006. Despite the traditional assumptions that cryptic species are ecologically equivalent due to their high phenotypic similarity, niche partitioning between these cryptic nematode species has been demonstrated with respect to microhabitat preferences (Guden et al., 2018), abiotic preferences and tolerances (De Meester et al., 2011, 2015b, competitive abilities (De Meester et al., 2011, 2015a, and dispersal strategies (De Meester et al., 2012. Furthermore, the existence of species-specific microbiomes has been illustrated in L. marina, which-among other things-may indicate that these very closely related species feed on different bacterial strains . ...
... Minimum juvenile development time and total fecundity were used as measures of individual fitness. Minimum juvenile development time was taken as the interval from the occurrence of the first juveniles until the appearance of the first F1-adult (De Meester et al., 2012). Minimum development time, the interval from the start of the incubation until the appearance of the first new adults, is often used as a measure for individual fitness (Moens and Vincx, 2000). ...
... Nevertheless, several studies have demonstrated enhanced herbivore growth and biomass accumulation with mixed diets of primary producers than with single-species diets (e.g., Pfisterer et al., 2003;Worm et al., 2006). However, in the rapidly changing and ephemeral habitat where L. marina lives, the coexistence of the cryptic species is likely not only determined by resource availability, but also by the responses of the cryptic species and their microbiomes to environmental changes (Derycke et al., 2006;De Meester et al., 2015a) and/or their ability to disperse to suitable patches with more favorable conditions (De Meester et al., 2012), such as a site with high resource diversity. ...
A Multi-Faceted Approach to Understand How Resource Diversity Can Mediate the Coexistence of Cryptic Marine Nematode Species
Article
Full-text available
  • Dec 2021
Based on the principle of competitive exclusion, species occupying the same ecological niche cannot stably coexist due to strong interspecific competition for resources. Niche diversification, for instance through resource partitioning, may alleviate competition. Here, we investigate the effects of resource diversity on foraging behavior, fitness and interspecific interactions of four cryptic bacterivorous nematode species (Pm I–IV) of the Litoditis marina species complex with sympatric field distributions. Three resource (bacteria) diversity levels (low, medium, high) were used as food treatments and compared to a treatment with only Escherichia coli as food. Differences in taxis to food existed between the cryptic species and between bacterial mixtures of different diversity: all the cryptic species except Pm I showed higher attraction toward medium-diversity food. Furthermore, the cryptic species of L. marina generally exhibited higher fitness on a more diverse food resource. Resource diversity also impacted the interspecific interactions between the cryptic species. Our results show that resource diversity can alter the interspecific interactions among the cryptic species of L. marina, indicating that competitive equilibria between species are very context-dependent. Although a considerable body of evidence supports the hypotheses (e.g., “variance-in-edibility” hypothesis and the “dilution hypothesis” or “resource concentration hypothesis”) which predict a negative impact on consumers when resource diversity is increased, the benefits of a diverse resource can outweigh these disadvantages by offering a more complete and/or complementary range of nutritional resources as suggested by the “balanced diet” hypothesis.
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... Differences in abiotic factors can include sympatric distributions but distinct (micro-)habitat preferences and tolerances, for example relating to depth, salinity, temperature, substrate, pollution and so on (De Meester et al. 2015b, Guden et al. 2018, Monteiro et al. 2018). On the other hand, differences in biotic factors can include differential resource use or life history traits, which can then have further knockon effects on the ecological interactions between the species (De Meester et al. 2012, Derycke et al. 2016. ...
... Extensive experiments on the cryptic Pm species have already revealed important ecological differences between them, including differences in their dispersal rates and abilities, as well as differential population responses to abiotic conditions (De Meester et al. 2012, 2015b. Interactions between the species are common, and affected by abiotic conditions, such as changes in temperature conditions from constant to fluctuating, leading for instance to a shift from commensalism to mutualism for two of the species (De Meester et al. 2015c). ...
... We wish to understand how these different factors affect the coexistence of the Litoditis cryptic complex, and how the species interactions are affected by changes in environmental conditions. Therefore, we focus on two sets of experiments on this cryptic complex conducted by De Meester et al.; the first relates to the differences in dispersal abilities between the cryptic species (De Meester et al. 2012, 2015a, and the second relates to changes in interaction between the species in response to changes in abiotic conditions (De Meester et al. 2011, 2015c. Given the stochasticity of these experimental systems, which are restricted to small population numbers in order to facilitate observation and data collection at the individual level, it is not reasonable to attempt a quantitative match of the dynamics with our mathematical model. ...
Untangling the mechanisms of cryptic species coexistence in a nematode community through individual‐based modelling
Article
  • Jan 2021
Cryptic species are morphologically identical but genetically distinct, and are prominent across numerous phyla. The coexistence of such closely related species on local scales would seem to run counter to traditional coexistence and competition theory; it has been hypothesized as a consequence of differences in their resource use or tolerances to environmental conditions. We developed an individual‐based model of a community of three cryptic Litoditis marina (nematode) species, to understand how individual‐level interspecific and intraspecific interactions might explain the coexistence of these closely related species. The model incorporates individuals’ reproduction, competition, dispersal, and resource use. Data characterizing the cryptic species (growth rates, dispersal ability, competitive interactions, and responses to changing environmental conditions) were obtained from laboratory experiments involving both mono‐ and multispecific nematode cultures, and are used to parameterize the model. Simulation studies are used to investigate which individual‐level mechanisms of dispersal and interaction lead to the characteristic population‐level patterns observed experimentally. Our results highlight the key role of intraspecific competition in mediating dispersal and therefore co‐occurrence of the cryptic species. The differences in dispersal also influence the response of the cryptic species to competition, a combination of factors that provides an explanation for their co‐occurrence. These results provide insights into how changes in individual‐level processes can be amplified to affect population‐level co‐occurrence. This article is protected by copyright. All rights reserved.
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... Inferred differences in the population histories between Clades A, B, and C support this conclusion. On the other hand, these lineages may well show ecological differences: in niche, as in cryptic species in the coral Pocillopora (Johnston et al., 2021); in environmental tolerances, as in the euryhaline colonial hydroid Cordylophora caspia (Folino-Rorem et al., 2009); or in life-history traits, as in the marine nematode Litoditis marina (DeMeester et al., 2012). "Autecological" studies of multiple, co-occurring cryptospecies within a morphospecies would be confounding. ...
The Bryozoan Cauloramphus magnus (Cheilostomata: Calloporidae) in Northern Japan Includes Multiple, Co-occurring Cryptic Species
Article
  • Feb 2023
The cheilostome bryozoan Cauloramphus magnus is common in the rocky intertidal habitat from southeastern Alaska to northern Japan. We examined its phylogeography by analyzing 576 bp of the mitochondrial COI (cox1) gene sequenced for 298 colonies from 16 localities in northern Japan. A maximum-likelihood phylogeny detected three main clades (A, B, C). Clades A and B occurred throughout the study area but differed in frequency, haplotype diversity, and haplotype distribution; each resolved into three divergent subclades (AI-III, BI-III). Clade A shared none among 15 haplotypes between the Pacific and Sea of Japan sides of Hokkaido. In contrast, Clade B (29 haplotypes) was thrice as common as Clade A among samples, with haplotype B28 common on both sides. Divergent Clade C (nine haplotypes) was detected only at Rumoi. K2P divergences of 12.3-28.3% among Clades A-C suggest these are distinct biological species, a conclusion supported by different inferred evolutionary histories. A bPTP species delimitation analysis indicated nine phylogenetic species among the sequences included in our phylogeny (AI-III, BI-III, C, and one specimen each from Alaska and the Commander Islands), with K2P divergences of 3.9-6.5% among subclades in A or B. Statistical and principal components analyses suggested weak morphological differentiation between Clades A + B and C, although overlapping ranges of measurements preclude identification to clade; these three clades are morphologically cryptic. For taxonomy, we suggest retaining the name C. magnus for lineages within this species complex across its range, followed by a clade designation, if known.
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... It has been shown that closely related, cryptic meiofaunal species can differ markedly in their competitive abilities, response to environmental stressors, and trophic preferences despite having almost identical morphologies (De Meester et al. 2012. This indicates that a considerable degree of niche segregation may be occurring, which would facilitate species coexistence. ...
Deep-Sea Meiofauna—A World on Its Own or Deeply Connected?
Chapter
  • Mar 2023
The deep sea is Earth’s most typical environment and meiofauna its most common and arguably its most diverse metazoan inhabitants. They are therefore key in understanding temporal and spatial patterns in biodiversity and biogeography and are major contributors to ecological processes and functions. Meiofauna are integral to deep-sea benthic communities, with numerous links to other benthic organisms and the interstitial environment, the habitat from where they experience life around them. Although many meiofaunal patterns and relations have been identified, limited progress has been made in answering questions as to “why” and “how” these patterns and relations exist or are formed and maintained, and in many cases such knowledge does not exist. In this chapter, we review the knowledge we do have and present interpretations and explanations that bring a better understanding of how meiofauna patterns in the deep sea can be explained in terms of processes and ecological interactions. We applied this approach in four distinct fields of study: trophic interactions; biodiversity and ecosystem function; distribution and diversity patterns; and connectivity patterns. All four illustrate the extent to which meiofauna relate to other biological components and the abiotic environment. Moreover, technological advances and the increase in multidisciplinary approaches (inherent to offshore deep-sea research) show that meiofauna studies are becoming better integrated with other fields of deep-sea research. Meiofauna, therefore, offer an exciting scientific and diverse future of discovery with research operating at the frontiers of deep-sea science.
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... It has been shown that closely related, cryptic meiofaunal species can differ markedly in their competitive abilities, response to environmental stressors, and trophic preferences despite having almost identical morphologies (De Meester et al. 2012. This indicates that a considerable degree of niche segregation may be occurring, which would facilitate species coexistence. ...
Freshwater Meiofauna—A Biota with Different Rules?
Chapter
  • Mar 2023
Great divergences arise when comparing the ecology of meiofauna in freshwater and marine ecosystems. Emphasizing the main differences between freshwater meiofauna and their marine counterparts, we will go on a stepwise journey through three major frontiers in freshwater research, which in turn are hierarchically interrelated: biodiversity, community organization (e.g. food webs structure), and ecosystem processes (e.g. metabolism and organic carbon breakdown). The starting point of this chapter is one of the utmost frontiers, both in marine and freshwater research: meiofaunal diversity. Especially in freshwater ecosystems diversity becomes evident since, here, habitats extend as highly disconnected biotopes, each characterized by an often fundamentally different biocenosis. From the biodiversity level, we move up the theoretical hierarchy to assess the role of meiofauna as an integral part of benthic food webs. Recent research underlines the role of freshwater meiofauna as highly connected nodes and shows their pivotal role in the transfer of energy and carbon along food chains. Distributed over all trophic levels, this structure contrasts with the prevailing conception of meiofauna in food webs, where meiofauna often are considered rather marginal units. Finally, we apply allometric principles from the metabolic theory of ecology in order to assess the role of freshwater meiofauna in the functioning of the benthic systems. With a novel modelling framework we develop an analytical perspective, showing that secondary production of micro- and meiobenthic communities can predict microbial decomposition rates within the benthic interface. Our results demonstrate that productive micro- and meiobenthos act as catalysers in the system of organic carbon breakdown and recycling. These findings underline the relevance of freshwater meiofauna within the biogeochemical carbon cycle. The mechanistic forces behind the processes involved require future experimental research.
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... Ambas aproximaciones parten de la hipótesis nula de que el taxón representa la misma especie. Al partir de un análisis molecular, se pone a prueba la monofilia recíproca, si se rechaza la hipótesis inicial, el siguiente paso es reevaluar la diagnosis morfológica, o buscar diferencias ecológicas (funcionales) (De Meester et al., 2012), y en última instancia, describir a los taxones que representan especies distintas (Pérez-Ponce de . Así, el uso de técnicas moleculares ayuda a corroborar la delimitación de especies ya descritas o reconocer especies nuevas . ...
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... Then, we opted for microcosms divided in directly connected sedimentary compartments with different qualities. To survive, populations can cope with adverse environmental conditions by dispersing away due to their restricted swimming abilities and their lack of pelagic stages (De Meester et al. 2012Derycke et al. 2013). Some studies (Bell 1988;Romney and Leiseboer 1989;Schratzberger et al. 2000a, b;Boufahja and Semprucci 2015;Boufahja et al. 2016) on vertical migration of meiofauna after burial or experimental studies using different types of sediments have proved that most species are able to migrate Responsible Editor: Philippe Garrigues * Fehmi Boufahja fehmiboufahja@yahoo.fr 1 upwards over a wide range of depths to reach the surface, showing the irrefutable influence of oxygenation on migration. ...
Experimental selection of Marylynnia puncticaudata (Cyatholaimidae, Nematoda) and effects of organic enrichment
Article
Full-text available
  • Feb 2021
  • ENVIRON SCI POLLUT R
Meiobenthic nematodes are well-known bioindicators in aquatic ecosystem health programs. However, the explored taxa are still limited and practically devoted to the community level. The present study provided a new method of experimental isolation of a species from a pristine nematofauna. In our method, the nematofauna faced two types of sediment, namely, the leaves of Posidonia oceanica and shells of Mytilus galloprovincialis, under controlled laboratory conditions, and several changes in species composition occurred through gradual selection of the most adaptable nematode taxa to the new environments, which were previously defaunated. We used the selected nematode taxon, Marylynnia puncticaudata (Cyatholaimidae), to examine the possible effects of organic enrichment, and the results clearly showed that the body size of the nematodes significantly increased and they became fat when after enrichment using a powder made of marine agar (1200 mg l⁻¹) and cuticles of Crangon crangon (900 mg l⁻¹), but their relative body growth showed no discernible changes.
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It's all about food: Environmental factors cause species‐specific dispersal
Article
Full-text available
  • Oct 2022
Dispersal is a vital component of the life history of nearly all organisms. The ability to disperse determines the distribution and abundance of a species and thus its community dynamic at different sites. The scientific challenge is to design standardized laboratory experiments that not only record the effects of single factors but also include the multicausal nature of dispersal. Here we tested the effect of the environmental factors density, food availability and predation, and the combinations thereof on the dispersal of five free‐living nematode species by performing experiments in two‐patched systems. We hypothesized that emigration is generally positively correlated with the intrinsic rate of natural increase and would decrease with increasing food availability and increase both with the presence of a predator and at higher initial population densities. These predictions were tested both using single‐species tests with laboratory cultures and using intact natural nematode communities to investigate whether environmental factors determine the composition of dispersing species. The results of our study revealed a positive correlation between dispersal and intrinsic growth ability, whereas the studied nematode species differed in their dispersal patterns, both under control conditions and in response to bottom‐up, top‐down, and density‐dependent stimuli. Despite the species‐specific differences in dispersal behavior in response to the environmental factors, the availability of food appeared as the main driver. This was particularly pronounced regarding a natural nematode community. Our experiments emphasize the central role of food availability in spatial structuring nematode communities.
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A new look into the small-scale dispersal of free-living marine nematodes
Article
Full-text available
  • Jul 2011
We tested experimentally the hypothesis that prevailing locomotion/feeding strategies and body morphology may lead to more active dispersal of free-living marine nematodes, besides passive transport. Neutral Red was applied to the sediment inside cores and the red plume formed during the flood tide was divided into near, middle, and distant zones. At 0.5 m and 1 m from the stained cores, sampling nets were suspended 5 and 10 cm above the sediment-water interface. Dispersion behaviors were defined as a function of a) the numbers of stained recaptured nematodes in comparison to their mean densities in the sediment, b) movement in the sediment or swimming in the water column, and c) body morphology. Tidal currents with average velocities of 9 cm/s resuspended the numerically dominant nematode taxa Sabatieria sp., Terschellingia longicaudata de Man, 1907, Metachromadora sp. and Viscosia sp. The recapture of stained nematodes as far as 2 m from the original stained cores showed that, despite their small body size, they can disperse through relatively large distances, either passively or actively, via the water column during a single tidal event. Recapture patterns in the sediment and in the water column indicate that nematode dispersal is directly influenced by their body morphology and swimming ability, and indirectly by their feeding strategies, which ultimately define their position in the sediment column. Besides stressing the role played by passive transport in the water column, our experiment additionally showed that mobility and feeding strategies also need to be considered as determinant of short-scale nematode dispersal.
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Ecological and Reproductive Differentiation in the Cryptic Species of the Hyla versicolor Complex (Hylidae)
Article
  • Dec 1968
The ecological and reproductive behavior of the cryptic species Hyla chrysoscelis and H. versicolor was examined in two sympatric localities and in one allopatric H. chrysoscelis locality. An analysis of the stomach contents of both species at one locality suggests that proportionately more H. chrysoscelis are eating arboreal insects, and proportionately more H. versicolor are eating terrestrial insects. The two species may be avoiding complete overlap of their niches in this way. There was a significant statistical, although not absolute, difference between the two species in the positions of the males calling around the breeding ponds; H. chrysoscelis tends to call from trees or bushes, while H. versicolor tends to call from the ground. A relationship between the ecological and reproductive behavior is discussed in terms of natural selection working in the same direction for both in each species. Limited relative humidity data, general geographic distribution of the two species, and the ground versus tree differences in food habits and calling position suggest that relative humidity is a key factor involved in these ecological and reproductive differences. It is thought that H. chrysoscelis can tolerate or may prefer lower relative humidities than H. versicolor. Two factors that were thought to affect the trill rates of both species were analyzed. High positive correlations between temperature and trill rate were found in regression analyses for both species. No correlation between body size and trill rate was found for either species. Population differences in the percentage of individuals using either the upper or lower harmonic as the dominant frequency of the mating call may prove to be of significance in the sympatric relations of the two species. Two populations of H. chrysoscelis sympatric with H. versicolor had mean trill rates 7% and 10% faster than the mean trill rate of an alloptric H. chrysoscelis population. It is suggested that reinforcement for differences in trill rate is occurring where the two species are sympatric.
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The Physiology of Life History Trade-Offs in Animals
Article
  • Jun 2001
  • Annu Rev Ecol Systemat
The functional causes of life history trade-offs have been a topic of interest to evolutionary biologists for over six decades. Our review of life history trade-offs discusses conceptual issues associated with physiological aspects of trade-offs, and it describes recent advances on this topic. We focus on studies of four model systems: wing polymorphic insects, Drosophila, lizards, and birds. The most significant recent advances have been: (a) incorporation of genetics in physiological studies of trade-offs, (b) integration of investigations of nutrient input with nutrient allocation, (c) development of more sophisticated models of resource acquisition and allocation, (d) a shift to more integrated, multidisciplinary studies of intraspecific trade-offs, and (e) the first detailed investigations of the endocrine regulation of life history trade-offs.
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The Ecology of Rafting in the Marine Environment. Ii. the Rafting Organisms and Community
Article
  • Jul 2005
  • OCEANOGR MAR BIOL
Rafting of marine and terrestrial organisms has been reported from a variety of substrata and from all major oceans of the world. Herein we present information on common rafting organisms and on ecological interactions during rafting voyages. An extensive literature review revealed a total of 1205 species, for which rafting was confirmed or inferred based on distributional or genetic evidence. Rafting organisms comprised cyanobacteria, algae, protists, invertebrates from most marine but also terrestrial phyla, and even a few terrestrial vertebrates. Marine hydrozoans, bryozoans, crustaceans and gastropods were the most common taxa that had been observed rafting. All major feeding types were represented among rafters, being dominated by grazing/boring and suspension-feeding organisms, which occurred on all floating substrata. Besides these principal trophic groups, predators/scavengers and detritus feeders were also reported. Motility of rafting organisms was highest on macroalgae and lowest on abiotic substrata such as plastics and volcanic pumice. Important trends were revealed for the reproductive biology of rafting organisms. A high proportion of clonal organisms (Cnidaria and Bryozoa) featured asexual reproduction, often in combination with sexual reproduction. Almost all rafting organisms have internal fertilisation, which may be due to the fact that gamete concentrations in the rafting environment are too low for successful fertilisation of external fertilisers. Following fertilisation, many rafting organisms incubate their offspring in/on their body or deposit embryos in egg masses on rafts. Local recruitment, where offspring settle in the immediate vicinity of parents, is considered an important advantage for establishing persistent local populations on a raft, or in new habitats. Some organisms are obligate rafters, spending their entire life cycle on a raft, but the large majority of reported rafters are considered facultative rafters. These organisms typically live in benthic (or terrestrial) habitats, but may become dispersed while being confined to a floating item. Substratum characteristics (complexity, surface, size) have important effects on the composition of the rafting community. While at sea, ecological interactions (facilitation, competition, predation) contribute to the community succession on rafts. Organisms capable to compete for and exploit resources on a raft (space and food) will be able to persist throughout community succession. The duration of rafting voyages is closely related to rafting distances, which may cover various geographical scales. In chronological order, three features of an organism gain in importance during rafting, these being ability to (1) hold onto floating items, (2) establish and compete successfully and (3) develop persistent local populations during a long voyage. Small organisms that do not feed on their floating substratum and, with asexual reproduction or direct development, combine all these features appear to be most suited for long-distance dispersal on rafts and successful colonisation after reaching new habitats. All available evidence suggests that rafting is an important process for the population dynamics of many organisms and that it also has had and continues to have a strong influence on coastal biodiversity.
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