Cryptic Assemblages Research Articles

Phylogeography of a widely distributed species reveals a cryptic assemblage of distinct genetic lineages needing separate conservation strategies

Genetic structure in broadly distributed herbs may be shaped by past climate events, leading to distinct genetic lineages, and possibly to different Evolutionary Significant Units (ESUs). We identified the potential glacial refugia, postglacial (re)colonization routes, contact zones and ESUs in the widespread but locally rare Silene nutans to propose appropriate conservation strategies related to migration history-related genetic structure. We sequenced four plastid DNA markers from 136 populations covering S. nutans European distribution range. We built a network on concatenated sequences using statistical parsimony and performed Bayesian and Maximum Likelihood analyses to build a phylogenetic tree. Haplotype genetic diversity and between-population differentiation (GST, NST) were calculated. Based on 23 plastid haplotypes, populations were ascribed to seven strongly differentiated genetic lineages. Potential refugia were identified: in the Iberian and Italian Peninsulas, expanding to south-western France and the Alps, respectively; in south-central France, reaching England and Belgium; an eastern refugium, following a north-westward expansion; in the Balkans, expanding to north-eastern Italy, and in the Carpathians. Several contact zones were identified. Silene nutans consists of a cryptic assemblage of genetically distinct taxa, with at least seven ESUs. Evaluating the distribution range, the abundance, and the conservation status of each ESU is necessary for the preservation of the S. nutans species complex at European and regional levels. Ex situ conservation and genetic restoration involving plant translocations must consider the phylogeographic history and the distinct genetic lineages to avoid the introduction of poorly adapted plants and outbreeding depression leading to non-viable hybrid progeny, especially in contact zones.

Colonization of coral rubble by motile cryptic animals: Differences between contiguous versus raised substrates from the bottom

Recent studies have demonstrated that interstices of coral rubble harbor rich and diverse assemblages of motile cryptic animals. Habitats of coral rubble are prone to frequent physical disturbances, so colonization is an important process to maintain the assemblages of these cryptic animals. In order to examine the pattern of colonization, field experiments were carried out using mesh traps with defaunated coral rubble: one treatment placed on the bottom and the other raised 15cm above the bottom (throughout as “raised”) to restrict colonizers to only organisms that are able to invade via the water column. Results of nMDS and PERMANOVA showed significant differences between the assemblages of the bottom and raised treatments. Species-specific variations in the rate of colonization, which were estimated by fitting the von Bertalanffy equation, contributed to the variations in the cryptic assemblages. Generally, decapods and gastropods colonized via the benthic pathway with colonizing individuals moving on the surface of the bottom substrate, while copepods and non-shelled gammarids colonized via the planktonic pathway. Variations in cryptic assemblages in coral rubble microhabitats may be partly due to differences in contributions via the two colonization pathways.

TALES FROM THE CRYPT: EARLY ADAPTATION OF CRYPTOBIONTIC SESSILE METAZOANS

Cryptic ecosystems of modern and ancient reefs contain substantial amounts of biodiversity. It remains uncertain, however, when and how metazoans adapted to such space. Early Cambrian reef systems witnessed the rise and fall of the earliest known cryptic sessile metazoans. Subsequent Middle Cambrian to Early Ordovician microbial-dominated reefs were generally devoid of true frame-building metazoans, as well as cryptic sessile fauna. The Early Ordovician microbial-siliceous sponge patch reefs of the Dumugol Formation, Korea represent one of the oldest in situ spiculate sponge-bearing cryptic communities exploiting intraskeletal cryptic environments. Less than half of these small millimeter- to centimeter-scale crypts contain low-diversity sessile cryptic assemblages of spiculate sponges and microbialites. The cryptic sponges that attach to the walls of the cavities or on top of internal sediments do not show any skeletal distortion at their contacts with host organisms. The spiculate sponges occur both in open spaces as well as in crypts, and are interpreted to be pioneers of intraskeletal crypts after the death of the cavity-providing organisms. The behavior of occupying transient cryptic habitats is interpreted as an incipient stage of sessile metazoan adaptation to a cryptic space by an opportunistic member of the epibenthic community. This resulted in the extension of the open surface community into crypts which occurred far in advance of the eventual establishment of obligate cryptic forms. The present study provides a critical link for establishing the origin and evolutionary history of early cryptic sessile metazoan adaptation.

Cryptic coral-crinoid “hanging gardens” from the Middle Devonian of southern Morocco

An unusual and exceptionally well preserved cryptic community of cnidarians, crinoids, sponges, and microbes developed in a submarine cavity of Middle Devonian age in the Hamar Laghdad area (Morocco). The biota encrusted the cavity roof and grew predominantly in an upside-down position, forming spectacular “hanging gardens.” The investigated assemblage differs strikingly from both its Paleozoic and modern analogues; it constitutes one of a very few known examples of fossil cryptic assemblages developed in relatively deep water settings, and is the first report of a cryptic paleoecosystem dominated by rugose corals. The results support the view that during the middle Paleozoic there was no distinct polarization between open-surface and cryptic faunas in deep-water environments, but keen competition for space already existed in Devonian cryptic assemblages. The regional species pool seems to have been the main determinant of the ecological succession and structure of this cryptic community.

Variations in cryptic assemblages in coral-rubble interstices at a reef slope in Ishigaki Island, Japan

The interstices of coral rubble provide a good refuge for cryptic small crustaceans and molluscs, which are important prey items for reef fishes. In this study, we focused on the assemblage composition of cryptic mobile species along the depth gradient at an outer reef slope. Traps with coral rubble (22 × 18 × 6 cm) were set at three sites at different depths, and mobile animals that colonized the traps were sorted. In total, 117 species of larger animals (mainly Decapoda and Gastropoda) were recorded: 71 species at the 3 m point, 53 species at the 11 m point, and 37 species at the 22 m point. On average, 260.3 individuals were captured in the traps at 3 m, while 95.3 and 57.8 individuals were captured at 11 and 22 m, respectively. MDS ordination showed that assemblage composition differed among the three sites. The most abundant species at the 3 m was the galathean crab Galathea mauritiana, followed by the gastropod Diala albugo. At 11 and 22 m, the galathean crab Sadayoshia edwardsii was most abundant. Thus, at the reef slope, the benthic assemblage was most diverse at the shallow site, and specific communities occurred at the three sites.

Importance of cryptic species for identifying ‘representative’ units of biodiversity for freshwater conservation

Nested systems of biodiversity classification are commonly used for designating protected area networks in terrestrial and marine realms. Whilst terrestrial-style protected areas are largely inappropriate for freshwater systems, the concepts of ‘representative’ biodiversity and ‘complementarity’ can be borrowed for freshwater conservation. Cryptic species are commonly found in freshwater macroinvertebrates and fish, and most have restricted distributions relative to the described conglomerate ‘species’. This indicates that ‘representative’ and therefore ‘complementary’ units of freshwater biodiversity may be smaller than previously appreciated. Using recently detected cryptic species in atyid shrimps from eastern Australia (Atyidae: Paratya australiensis, Caridina mccullochi and C. indistinca), we tested predictions about regional patterns of cryptic assemblage structure, endemism and Phylogenetic Diversity (PD) at the river scale, and discussed their implications for freshwater conservation. Patterns of distribution in these cryptic shrimp species largely corresponded with published distributional patterns of cryptic species in several freshwater fish in eastern Australia, and indicated the presence of four putative ecoregions within a previously recognised freshwater fish province (Eastern Province). However, some rivers had pronounced cryptic endemism, suggesting that rivers may not be ‘representative’ of one another’s biodiversity even within ecoregions. PD and endemism were largely correlated with one another, as endemics typically co-occurred with widespread species at the river scale. This study indicates that cryptic species can contribute to defining patterns of biodiversity at nested spatial scales that may be important for freshwater conservation.

Cryptic assemblages in coral-rubble interstices along a terrestrial-sediment gradient

The assemblage composition of cryptic mobile animals inhabiting coral rubble was sampled using mesh traps containing clean coral rubble, and used as indicators of land-based pollution at 14 sites in three coral lagoons at Ishigaki Island, southern Japan. Cluster analyses identified three groups of large mobile animal assemblages (molluscs, echinoderms, fishes, decapod and stomatopod crustaceans). Using a distance-based redundancy analysis (db-RDA) there was a significant relationship between the assemblage composition and environmental variables. The 1st axis of the db-RDA ordination was regarded as the land-based pollution gradient because of the strong relationship with silicate sediment, turbidity, and salinity, indicating effects of terrestrial-sediment runoff. Species response curves were derived from a plot of the number of individuals against the 1st axis of the db-RDA sites sample score. The response curves of Galathea mauritiana, an indicator species for the intermediate sites, were unimodal along the land-based pollution gradient. This study demonstrates the use of traps containing clean coral rubble for nondestructive quantitative sampling and environmental monitoring in coral lagoons, and their potential for monitoring changes in the reef environment.

A new equatorial, very shallow marine sclerozoan fauna from the Middle Jurassic (late Callovian) of southern Israel

Tropical Jurassic sclerozoan faunas are poorly known, yet they are critical to our understanding of Jurassic biogeography and the evolution of hard substrate communities. A diverse assemblage of hard substrate fossils is here described from subunits 53 and 54 of the upper Matmor Formation (Callovian) of Hamakhtesh Hagadol in the Negev Desert of southern Israel. This region was on, or very, near the equator during the Middle Jurassic. The fauna is dominated by flat, platter-shaped sponges ( Actostroma?) and scleractinian corals ( Microsolena), some of which have the depressed centers and raised rims of “microatolls” which form today in the shallowest subtidal zone associated with reef systems. The coral and calcareous sponge platters are encrusted on their top surfaces by one species of serpulid worm and many small coral and sponge recruits with narrow attachments and mushroom-shaped or conical skeletons growing upwards. The undersurfaces of the platters are encrusted by another serpulid species, at least two calcareous sponges, rare cyclostome bryozoans, oysters, plicatulid bivalves, and numerous thecideide brachiopods (the first known from the Jurassic of the region). The upper and undersurfaces of the platters are often bored by bivalves, forming the ichnospecies Gastrochaenolites torpedo. These borings were occasionally reoccupied by a nestling mytilid bivalve on the undersurfaces of the skeletal platters. This encrusting fauna of the Matmor Formation apparently lived in a shallow lagoon on the landward side of a coral reef. The fossils in the surrounding muddy sediments are primarily echinoids, oysters, and rhynchonellid and terebratulid brachiopods. This sclerozoan fauna is an evidence that Jurassic tropical hard substrate faunas were serpulid-rich and bryozoan-poor as predicted, but more diverse (at twelve species) than expected. This community was also ecologically divided into open and cryptic assemblages like its Jurassic equivalents in the temperate and subtropical waters of Europe and North America.

Quantitative characterization of shallow marine benthic assemblages at Ryder Bay, Adelaide Island, Antarctica

Non-destructive photographic techniques are valuable for surveying benthic epifauna in sensitive areas. Inherent in these techniques, however, are selectivity biases related to the scale at which surveys are conducted. Such biases have not been addressed for surveys of marine benthos. The present study surveyed epifaunal assemblages at two depths (8 m and 20 m) and three locations close to Rothera Point, Adelaide Island, Antarctica. Two scales of photographic sampling were employed in order to encompass a broad range of taxon sizes and distributions, and their parallel use allowed qualitative and quantitative comparisons to be made between results from each scale. An additional physical sampling element was incorporated to assess sessile cryptic assemblages. A total of 79 faunal taxa from 10 phyla, together with 6 algal taxa, were recorded in the survey. Echinoderms were the most speciose group at both photographic scales, whereas cryptic assemblages were dominated by bryozoans. There were clear resolution-related differences between scales but all three methods revealed pronounced differences in assemblages by depth and location. Assemblages at both depths were notable for consistently high densities (~100 individuals m−2) of the regular echinoid Sterechinus neumayeri, and at 8 m for high densities (~100 individuals m−2) of the limpet Nacella concinna. The results emphasise the general requirement for sampling methodologies to be matched to the size spectra of the organisms under study and, more specifically, highlight the need for studies to assess the relative importance of biotic and physical factors in structuring the Antarctic benthos.