Gerhard Pohle

ACCURACY AND STANDARDIZATION OF BRACHYURAN LARVAL DESCRIPTIONS

Summary There is a need for improvement and standardization in larval descriptions for them to become useful not only for identification purposes but also in comparative and phylogenetic studies. Details of the rearing technique and equipment used should be given, the spent female crab and representative larval stages need to be deposited at a national museum and a minimum of five specimens of each stage should be used for meristic and morphometric criteria. Diagnostic features of the carapace, all appendages, abdomen, and other characters that are to be included in a standard larval description are presented with specifications concerning format and sequence of substructures. Typical configurations of larval structures are given and some possible exceptions are described. Guidelines for illustrations including the preparation, size, sequence and arrangement of figures are provided.

Phylogenetic analysis of the Pinnotheridae (Crustacea, Brachyura) based on larval morphology, with emphasis on the Dissodactylus species complex

Comparative larval morphology was used to elucidate phylogenetic relationships within the Pinnotheridae and the Dissodactylus species complex. Within the family, seven zoeal and six megalopal characters suggested two equally parsimonious phylogenetic hypotheses for pinnotherid larvae, both with Ostracotheres tridacnae representing the sister group for the Dissodactylus complex. Results indicated that the genus Pinnotheres is a polyphyletic taxon, and that the traditional subfamilial arrangement comprises paraphyletic taxa within the subfamilies Pinnotherinae and Pinnothereliinae. Certain evidence has suggested that Fabia and Juxtafubia should be excluded from the Pinnotherinae and placed into the Pinnothereliinae. Larval and adult morphology suggested that Pinnotheres politus should be included within Tumidotheres. The phylogenetic analysis within the Dissodactylus complex involved one zoeal and 16 megalopal characters. Results suggested a single phylogenetic hypothesis based on larval morphology. Combining adult morphology with larval evidence resulted in two equally parsimonious phylogenetic hypotheses, one of which agreed with a previously suggested hypothesis based only on adult characters.

Large-scale spatial distribution patterns of echinoderms in nearshore rocky habitats

This study examined echinoderm assemblages from nearshore rocky habitats for large-scale distribution patterns with specific emphasis on identifying latitudinal trends and large regional hotspots. Echinoderms were sampled from 76 globally-distributed sites within 12 ecoregions, following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). Sample-based species richness was overall low (<1–5 species per site), with a total of 32 asteroid, 18 echinoid, 21 ophiuroid, and 15 holothuroid species. Abundance and species richness in intertidal assemblages sampled with visual methods (organisms >2 cm in 1 m2 quadrats) was highest in the Caribbean ecoregions and echinoids dominated these assemblages with an average of 5 ind m−2. In contrast, intertidal echinoderm assemblages collected from clearings of 0.0625 m2 quadrats had the highest abundance and richness in the Northeast Pacific ecoregions where asteroids and holothurians dominated with an average of 14 ind 0.0625 m−2. Distinct latitudinal trends existed for abundance and richness in intertidal assemblages with declines from peaks at high northern latitudes. No latitudinal trends were found for subtidal echinoderm assemblages with either sampling technique. Latitudinal gradients appear to be superseded by regional diversity hotspots. In these hotspots echinoderm assemblages may be driven by local and regional processes, such as overall productivity and evolutionary history. We also tested a set of 14 environmental variables (six natural and eight anthropogenic) as potential drivers of echinoderm assemblages by ecoregions. The natural variables of salinity, sea-surface temperature, chlorophyll a, and primary productivity were strongly correlated with echinoderm assemblages; the anthropogenic variables of inorganic pollution and nutrient contamination also contributed to correlations. Our results indicate that nearshore echinoderm assemblages appear to be shaped by a network of environmental and ecological processes, and by the differing responses of various echinoderm taxa, making generalizations about the patterns of nearshore rocky habitat echinoderm assemblages difficult.

Spatial relationships between polychaete assemblages and environmental variables over broad geographical scales

This study examined spatial relationships between rocky shore polychaete assemblages and environmental variables over broad geographical scales, using a database compiled within the Census of Marine Life NaGISA (Natural Geography In Shore Areas) research program. The database consisted of abundance measures of polychaetes classified at the genus and family levels for 74 and 93 sites, respectively, from nine geographic regions. We tested the general hypothesis that the set of environmental variables emerging as potentially important drivers of variation in polychaete assemblages depend on the spatial scale considered. Through Morans eigenvector maps we indentified three submodels reflecting spatial relationships among sampling sites at intercontinental (>10000 km), continental (1000–5000 km) and regional (20–500 km) scales. Using redundancy analysis we found that most environmental variables contributed to explain a large and significant proportion of variation of the intercontinental submodel both for genera and families (54% and 53%, respectively). A subset of these variables, organic pollution, inorganic pollution, primary productivity and nutrient contamination was also significantly related to spatial variation at the continental scale, explaining 25% and 32% of the variance at the genus and family levels, respectively. These variables should therefore be preferably considered when forecasting large-scale spatial patterns of polychaete assemblages in relation to ongoing or predicted changes in environmental conditions. None of the variables considered in this study were significantly related to the regional submodel.

Phylogeny of the Pinnotheridae: larval and adult evidence, with emphasis on the evolution of gills

Summary The Pinnotheridae represents a diverse group of very small crabs associated with other invertebrates. Here we show that, among the brachyurans, pinnotherids display the greatest diversity in numbers of gills and gill grooming appendages, with a continuous spectrum ranging from eight to three gills per branchial chamber, on as many as five to as few as two gill bearing appendages. There is no linear relationship between the reduction of gill numbers and size of the crabs. The reduction of gills took place in both anterior and posterior thoracic regions. Also, unlike other Brachyura, some pinnotherids lack a gill grooming appendage on maxilliped 2. These taxa are characterized by four or fewer gills per branchial chamber. In the interest of clarifying the systematic position of species and genera within the Pinnotheridae, 13 adult characters related to gill formulas, morphology of grooming appendages and setae, and hosts were used with 13 larval characters to determine sister group relationships amo...

Patterns of Spatial Variation of Assemblages Associated with Intertidal Rocky Shores: A Global Perspective

Assemblages associated with intertidal rocky shores were examined for large scale distribution patterns with specific emphasis on identifying latitudinal trends of species richness and taxonomic distinctiveness. Seventy-two sites distributed around the globe were evaluated following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). There were no clear patterns of standardized estimators of species richness along latitudinal gradients or among Large Marine Ecosystems (LMEs); however, a strong latitudinal gradient in taxonomic composition (i.e., proportion of different taxonomic groups in a given sample) was observed. Environmental variables related to natural influences were strongly related to the distribution patterns of the assemblages on the LME scale, particularly photoperiod, sea surface temperature (SST) and rainfall. In contrast, no environmental variables directly associated with human influences (with the exception of the inorganic pollution index) were related to assemblage patterns among LMEs. Correlations of the natural assemblages with either latitudinal gradients or environmental variables were equally strong suggesting that neither neutral models nor models based solely on environmental variables sufficiently explain spatial variation of these assemblages at a global scale. Despite the data shortcomings in this study (e.g., unbalanced sample distribution), we show the importance of generating biological global databases for the use in large-scale diversity comparisons of rocky intertidal assemblages to stimulate continued sampling and analyses.

Searching for larval support for majoid families (Crustacea: Brachyura) with particular reference to Inachoididae Dana, 1851

Summary We re-evaluated the larval support for families within majoids using the Wilcoxon signed-rank test with emphasis on Inachoididae. To accomplish our objectives, we added 10 new taxa, two of which are traditionally assigned to the family of special interest, to a previous larval database for majoids, and re-appraised the larval characters used in earlier studies. Phylogenetic analysis was performed with PAUP* using the heuristic search with 50 replicates or the branch-and-bound algorithm when possible. Multi-state transformation series were considered unordered; initially characters were equally weighted followed by successive weighting, and trees were rooted at the Oregoniidae node. Ten different topological constraints were enforced for families to evaluate tree length under the assumption of monophyly for each taxonomic entity. Our results showed that the tree length of most constrained topologies was not considerably greater than that of unconstrained analysis in which most families nested as paraphyletic taxa. This may indicate that the present larval database does not provide strong support for paraphyly of the taxa in question. For Inachoididae, although the Wilcoxon signed-rank test rejected a significant difference between unconstrained and constrained cladograms, we were unable to provide a single synapomorphy for this clade. Except for the conflicting position of Leurocyclus and Stenorhynchus, the two clades correspond to the traditional taxonomic arrangement. Among inachoidids, the clade (Anasimus (Paradasygyius (Collodes +Pyromaia))) is supported, whereas for inachids, the clade (Inachus (Macropodia +Achaeus)) is one of the most supported clades within majids. As often stated, only additional characters will provide a better test for the monophyly of Inachoididae and other families within Majoidea.

The use of structural reduction in phylogenetic reconstruction of decapods and a phylogenetic hypothesis for 15 genera of Majidae: testing previous larval hypotheses and assumptions

Summary Using larval data of zoeae from selected genera of majids, we determined tree topologies, levels of homoplasy, and frequencies of reduction under three different assumptions of character argumentation: ordered reduction events, unordered reduction events, and outgroup comparison. Under each assumption we provided a phylogenetic hypothesis for some majid genera and evaluated the assumption that structural reduction can be assumed a priori as a criterion to infer character transformation polarity in phylogenetic reconstruction of decapods. The results indicate that the a priori assumption of “reduction” as the derived condition is not justified because under this assumption, reduction is not always maintained throughout the resulting phylogenetic hypothesis. Furthermore, we also found that this criterion fails to provide the most parsimonious explanation of the data set. Therefore, we reject the use a “reduction=derived” criterion to infer polarity in phylogenetic reconstruction. Phylogenetic analys...

On the Larval Stages of Macrocoeloma Diplacanthum (Decapoda: Brachyura: Majidae), and a Review of Mithracine Phylogenetic Aspects

Abstract Larval development of Macrocoeloma diplacanthum (Stimpson) consists of two zoeal stages, followed by the megalopa. Each larval stage is described in detail. The duration of the zoeal stages was 2–3 (2.4 ± 0.5) and 3–4 (3.5 ± 0.5) days for the first and second zoea, respectively, the megalopa phase appearing 6–8 (7.0 ± 0.5) days after hatching. Unlike for other majids, zoeal stages of M. diplacanthum can be readily distinguished by their distended forehead with strong underlying muscle bands, undercut dorsal carapace spine, and spine on the terminal endopod segment of the first maxilliped. No other known mithracine or majid zoeae exhibit this combination of features. Our zoeal account of M. diplacanthum from Mexico is remarkably consistent with Floridian specimens previously described. However, we have found some differences between descriptions, which could be attributed to natural variation or inadequate description. Previous attempts to evaluate the relationships within Mithacinae have been based on larval characters widely distributed throughout Majidae and therefore are considered inadequate to infer sister-group relationships. The phylogenetic analysis of majids suggested that the position of Mithracinae is still uncertain, as is its monophyletic status. We recommend that additional characters, particularly of the megalopa phase, be sought for a better resolution of majid evolutionary history.

Zoeal stages and megalopa of Mithrax hispidus (Herbst, 1790) (Decapoda: Brachyura: Majoidea: Mithracidae): A reappraisal of larval characters from laboratory cultured material and a review of larvae of the Mithrax-Mithraculus species complex

Summary Mithrax hispidus (Herbst, 1790) is a mithracid majoid crab occurring on sand, corals and rocks in waters of the western Atlantic. Larval development consists of two zoeal stages and a megalopa. All larval stages are described in detail based on multiple cultures. Prior to this study, larvae of M. hispidus were considered to be different and grouped separately from most other larvae of Mithrax, primarily based on setation. A detailed morphological examination, based on the same specimens used for the first description, revealed that the inclusion of M. hispidus in a separate group is not valid as zoeae now fully agree with the morphological characteristics defined for the other group of five Mithrax species, including M. pleuracanthus, M. verrucosus, M. caribbaeus, M. coryphe, and M. forceps. This illustrates the importance of precisely recording morphological details such as setation, which may otherwise lead to incorrect interpretations with regard to perceived taxonomic affinities. A comparison of larvae of the Mithrax-Mithraculus species complex does not support separation into two genera. Larval evidence supports the recently suggested adult-based synonymization of M. caribbaeus with M. hispidus.