Koenraad Martens

Body size and dispersal mode as key traits determining metacommunity structure of aquatic organisms

Relationships between traits of organisms and the structure of their metacommunities have so far mainly been explored with meta-analyses. We compared metacommunities of a wide variety of aquatic organism groups (12 groups, ranging from bacteria to fish) in the same set of 99 ponds to minimise biases inherent to meta-analyses. In the category of passive dispersers, large-bodied groups showed stronger spatial patterning than small-bodied groups suggesting an increasing impact of dispersal limitation with increasing body size. Metacommunities of organisms with the ability to fly (i.e. insect groups) showed a weaker imprint of dispersal limitation than passive dispersers with similar body size. In contrast, dispersal movements of vertebrate groups (fish and amphibians) seemed to be mainly confined to local connectivity patterns. Our results reveal that body size and dispersal mode are important drivers of metacommunity structure and these traits should therefore be considered when developing a predictive framework for metacommunity dynamics.

The ecology of ostracodes (Ostracoda, Crustacea) in western Mongolia

Aquatic biota in Central Asia witnesses and faces a changing environment. Because ostracodes contribute to both extant and fossil lacustrine diversity, they can be used to track evolution in water quality. Living ostracode communities in a variety of aquatic habitats of western Mongolia were analyzed in relation to environmental and hydrochemical variables of those habitats, based on presence/absence data from net samples. The sampled water bodies represent broad gradients in ionic concentration and composition. Ostracode community composition of springs differed from all other sampled habitats, which was also reflected in CCA analyses. Our data indicated that the ostracode fauna of western Mongolia shows a high response to calcium content, alkalinity, salinity, temperature, nutrients, and altitude. Species composition and diversity seem to be determined by solute evolution dominated by Ca-depletion. In general, this seems to be an important regulator of lacustrine ostracode species composition in several semi-arid regions. Binary logistic regression was used to predict the occurrence of the most common species with a minimal set of environmental variables. The resulting models showed on average low performance, and mainly demonstrated the potential of such modeling to predict the distribution of typical bio-indicator species.

The freshwater microcrustacea of Easter Island

The ‘Cladocera’, Copepod and Ostracod fauna of Easter Island amounts to only five species. Three of these are wide-ranging, and four are cyclic parthenogens or at least capable of parthenogenesis. Two, the Cladoceran Alona weinecki and the Ostracod Sarscypridopsis sp., are more interesting from a biogeographic point of view, because restricted (apart from Easter Island) to the subantarctic. It is argued that this is strong evidence of their introduction by man, not by ‘natural’ passive dispersal.

Water quality and diversity of the Recent ostracod fauna in lowland springs from Lombardy (northern Italy)

The Po river plain (northern Italy) is delimited to two mountain ridges, the Alps and the Apennines. It hosts peculiar lowland man-modified springs, locally known as “fontanili”, which originate from natural resurgences occurring along the alluvial fans of the main watercourses, namely in the transition zone from the higher to lower plain which is characterized by changes in slope profile and sediment granulometry. These habitats usually show low variation in hydrological, hydrochemical and thermal conditions throughout the year. Twenty-eight springs, located in the provinces of Lodi and Cremona (Lombardy) in the alpine sub-catchment of the Po river were sampled in summer and autumn of 2004. Twenty-three of them were typical alluvial-fan springs, while the remaining five were terrace springs. The two groups of springs showed marked differences in their hydrochemical and hydrological characteristics. Sixteen ostracod species in three families (Candonidae, Ilyocyprididae, and Cyprididae) were identified. The most frequent species were Cypria ophtalmica (19 sites), Herpetocypris reptans (16), and Prionocypris zenkeri (13). Five species were found only once: Chlamydotheca incisa, Scottia pseudobrowniana, Pseudocandona compressa and Candona neglecta. Up to 6 taxa were recorded from a single site and the average number of taxa for each site was c. 3. The associations among ostracod taxa and their occurrence in relation to environmental factors were examined. Finally, the results of this survey were compared with a similar study previously conducted in 31 alluvial fan springs of the apennine sub-catchment of the Po river.

Preface: Cladocera crustaceans: sentinels of environmental change

Growing awareness of the negative impacts of global change urges scientists to look for adequate means to assess past and ongoing environmental change. The extent and dynamics of natural ecosystem variability is not yet fully clear, though understanding of this variability is crucial for predicting future trends (IPCC, 2007). Paleolimnological records holding valuable proxy information in the form of sediment features, geochemical records and microand macrofossil assemblages, can complement observational data by extending timescales, integrating sub-annual variability and expanding the range of sites that can be studied (Battarbee et al., 2005). Modern limnological time-series, though limited in space and time, can still add crucial information to these surveys. Similarly, in situ and laboratory experiments can complement paleolimnological approaches by improving our mechanistic understanding of the relationship between proxy indicators and their environment. Cladocera (Crustacea: Branchiopoda; water fleas) play a key role in freshwater ecosystems because of their pivotal position in the food web, sandwiched between top-down regulators (fish and invertebrate predators) and bottom-up factors (phytoplankton). The intermediary position occupied by cladocerans underlies their significance for nutrient cycling in freshwaters (Jarvinen & Salonen, 1998; Urabe et al., 2002) and as sentinels of environmental change (Jeppesen et al., 2001; Korhola & Rautio, 2001; Kurek et al., 2010). Subfossil cladocerans (typically Bosminidae, Chydoridae and Daphniidae) appear in lake sediments mainly in disarticulated body parts, such as head shields, carapaces and postabdomens, or as epphipia (a structure that protects diapausing eggs). The taxonomic composition of these remains has been used to track past changes in the environment, including eutrophication (Brodersen et al., 1998; Shumate et al., 2002; de Eylo et al., 2003; Davidson et al., 2007; Chen et al., 2010), acidification (Paterson, 1994; Jeziorski et al., 2008), lake water calcium decline (Jeziorski et al., 2008), lake levels (Korhola et al., 2000, 2005) and climate (Lotter et al., 2000; Kattel et al., 2008). In addition, the taxonomic composition of cladocerans shows a strong response to biotic factors that can vary with lake trophic state, such as fish density (Jeppesen et al., 1996, 2001; Finney et al., 2000) and submerged macrophytes (Davidson et al., 2007). Cladocera-based reconstructions have not remained qualitative only, but the strong link between cladoceran Guest editors: H. Eggermont & K. Martens / Cladocera as indicators of environmental change.

On a new species and genus in the Cypridini (Crustacea, Ostracoda, Cyprididae) from South Africa, with a phylogenetic analysis of the tribe and a discussion on the genus concept in this group

The present paper describes Mnementh brennei n. sp. n. gen., a new non‐marine ostracod species and genus from temporary wetlands in the Western Cape Province (South Africa). The new genus is the fifth in the subfamily Cypridinae and a phylogenetic analysis using morphological characters demonstrates that it is most closely related to its putative sister taxon Pseudocypris. Apart from this cluster, the phylogenies are not at all robust and this is to all probability due to the incongruent (mosaic) evolution amongst the different characters in valve and soft part modules. Implications of such incongruent evolution of characters for the concept of genera in this group are discussed.

Early release of eggs and embryos in a brooding ancient asexual ostracod: brood selection or a gambling strategy to increase fecundity?

Asexual lineages lack the means to purge their genomes of (deleterious) mutations through recombination. Evolutionary theory thus predicts that such lineages will be prone to early extinction. In brooding animals, brood selection might provide a mechanism to counter the accumulation of mutations. Of the three putative ancient asexual animal groups, only the darwinulid ostracods are brooders. Here, we test the incidence of egg and juvenile abortion in a darwinulid species, Penthesilenula brasiliensis, under two temperature treatments. Part of the offspring is released without brooding (close to 30% in one treatment). The majority of these aborted eggs hatches and develops. As it is unlikely that females are such bad judges of offspring quality, either the surviving animals will present deficiencies later on in development (brood selection) or early egg release can be a (bet-hedging) strategy to increase fecundity in favourable conditions.

On Afrocypris barnardi G. O. Sars, 1924 (Ostracoda), a second giant ostracode with additional appendages

[Afrocypris barnardi G. O. Sars, 1924, a giant temporary pool ostracode from South Africa, is here redescribed, based on new material. It is only the second time that this species has been found. The present morphological analyses show that the copulatory appendages of both sexes have unusual characteristics. In the female, at least three paired appendage-like structures (R-appendages) are associated with the Female Reproductive Organ (FRO). This is the second time that such structures are described from non-marine ostracodes, Liocypris grandis (G. O. Sars, 1924) having six pairs of such structures. The male copulatory organs have a Penile Attachment uniting the proximal sides of both hemipenes, and in Afrocypris barnardi an asymmetrical, finger-like structure is associated with this PA.The discovery of female R-appendages in a second species strengthen the interpretation of these structures as (part of) true appendages, and reinforces the hypothesis that the FRO is homologous to more than one ancestral somite. However, it remains unclear how many body segments are involved in the origin of the FRO, and three, five, or even six somites are all possible. In addition, these R-appendages can be ancestral, atavistic, or even apomorphic. The position of the two taxa with such appendages in a phylogeny of the Cyprididae as a whole will constitute a test to discriminate between these three possibilities. Basierend auf neuen Funden wird Afrocypris barnardi G. O. Sars, 1924, eine Gros-Ostracodenart aus ephemeren Kleingewassern Sudafrikas, hier wiederbeschrieben. Die Funde stellen erst den zweiten Nachweis dieser Art dar. Die neue morphologische Untersuchung zeigt, das die Kopulationsorgane beider Geschlechter ungewohnliche Merkmale aufweisen. Dem externen weiblichen Kopulationsapparat (FRO) sind mindestens drei paarige, extremitatenartige Anhange (R-Appendages) zugeordnet. Erst zum zweiten Mal werden solche Strukturen fur eine Suswasserostracodenart nachgewiesen: Liocypris grandis (G. O. Sars, 1924) besitzt sechs solcher Anhange.Das Kopulationsorgan des Mannchens besitzt einen Anhang (PA), welcher die proximalen Bereiche der beiden Hemipenes verbindet. Auf diesem Anhang inseriert bei Afrocypris barnardi zudem eine asymmetrische fingerformige Struktur.Die Entdeckung von zusatzlichen extremitatenartigen Anhange des weiblichen Kopulationsapparates in einer zweiten Ostracodenart verstarkt ihre Interpretation als (Teile von) echte(n) Extremitaten und unterstutzt die Hypothese, das der weibliche Kopulationsapparat mehr als einem ursprunglichen Segment homolog ist. Allerdings bleibt unklar, wieviele Korpersegmente in die Bildung des Kopulationsapparates involviert sind; drei, funf oder sogar sechs Segmente waren denkbar. Zudem konnen diese zusatzlichen Anhange sowohl ancestrale, als auch atavistische oder apomorphe Merkmale darstellen. Erst die Positionierung der beiden Taxa mit solchen Anhangen in einer Phylogenie der Cyprididae wird eine Entscheidung ermoglichen., Afrocypris barnardi G. O. Sars, 1924, a giant temporary pool ostracode from South Africa, is here redescribed, based on new material. It is only the second time that this species has been found. The present morphological analyses show that the copulatory appendages of both sexes have unusual characteristics. In the female, at least three paired appendage-like structures (R-appendages) are associated with the Female Reproductive Organ (FRO). This is the second time that such structures are described from non-marine ostracodes, Liocypris grandis (G. O. Sars, 1924) having six pairs of such structures. The male copulatory organs have a Penile Attachment uniting the proximal sides of both hemipenes, and in Afrocypris barnardi an asymmetrical, finger-like structure is associated with this PA.The discovery of female R-appendages in a second species strengthen the interpretation of these structures as (part of) true appendages, and reinforces the hypothesis that the FRO is homologous to more than one ancestral somite. However, it remains unclear how many body segments are involved in the origin of the FRO, and three, five, or even six somites are all possible. In addition, these R-appendages can be ancestral, atavistic, or even apomorphic. The position of the two taxa with such appendages in a phylogeny of the Cyprididae as a whole will constitute a test to discriminate between these three possibilities. Basierend auf neuen Funden wird Afrocypris barnardi G. O. Sars, 1924, eine Gros-Ostracodenart aus ephemeren Kleingewassern Sudafrikas, hier wiederbeschrieben. Die Funde stellen erst den zweiten Nachweis dieser Art dar. Die neue morphologische Untersuchung zeigt, das die Kopulationsorgane beider Geschlechter ungewohnliche Merkmale aufweisen. Dem externen weiblichen Kopulationsapparat (FRO) sind mindestens drei paarige, extremitatenartige Anhange (R-Appendages) zugeordnet. Erst zum zweiten Mal werden solche Strukturen fur eine Suswasserostracodenart nachgewiesen: Liocypris grandis (G. O. Sars, 1924) besitzt sechs solcher Anhange.Das Kopulationsorgan des Mannchens besitzt einen Anhang (PA), welcher die proximalen Bereiche der beiden Hemipenes verbindet. Auf diesem Anhang inseriert bei Afrocypris barnardi zudem eine asymmetrische fingerformige Struktur.Die Entdeckung von zusatzlichen extremitatenartigen Anhange des weiblichen Kopulationsapparates in einer zweiten Ostracodenart verstarkt ihre Interpretation als (Teile von) echte(n) Extremitaten und unterstutzt die Hypothese, das der weibliche Kopulationsapparat mehr als einem ursprunglichen Segment homolog ist. Allerdings bleibt unklar, wieviele Korpersegmente in die Bildung des Kopulationsapparates involviert sind; drei, funf oder sogar sechs Segmente waren denkbar. Zudem konnen diese zusatzlichen Anhange sowohl ancestrale, als auch atavistische oder apomorphe Merkmale darstellen. Erst die Positionierung der beiden Taxa mit solchen Anhangen in einer Phylogenie der Cyprididae wird eine Entscheidung ermoglichen.]

Distribution and community structure of Ostracoda (Crustacea) in shallow waterbodies of southern Kenya

The current study presents the ostracod communities recovered from 26 shallow waterbodies in southern Kenya, combined with an ecological assessment of habitat characteristics. A total of 37 waterbodies were sampled in 2001 and 2003, ranging from small ephemeral pools to large permanent lakes along broad gradients in altitude (700–2 800 m) and salinity (37–67 200 µS cm−1). Between 0 and 12 species were recorded per site. Lack of ostracods was associated with either hypersaline waters, or the presence of fish in fresh waters. Three of the 32 recovered ostracod taxa, Physocypria sp., Sarscypridopsis cf. elizabethae and Oncocypris mulleri, combined a wide distribution with frequent local dominance. Canonical correspondence analysis on species–environment relationships indicated that littoral vegetation, altitude, surface water temperature and pH best explain the variation in ostracod communities. Presence of fish and water depth also influence species occurrence, with the larger species being more common in shallow waterbodies lacking fish. Based on Chao’s estimator of total regional species richness, this survey recovered about two-thirds (60–68%) of the regional ostracod species pool. Scanning electron micrographs (SEM) of the valve morphology of 14 ostracod taxa are provided, in order to facilitate their application in biodiversity and water-quality assessments and in palaeoenvironmental reconstruction.