Brown Color Morphs Research Articles

Micro‐ and macroclimate interactively shape diversity, niches and traits of Orthoptera communities along elevational gradients

AbstractAimTemperature is one of the main drivers shaping species diversity and assembly processes. Yet, site‐specific effects of the local microclimate on species and trait compositions of insect communities have rarely been assessed along macroclimatic temperature clines.LocationBavarian Alps, Germany.MethodsBayesian joint species distribution models were applied to investigate how ecological and morphological traits drive variation in the climatic niches of 32 Orthoptera species on 93 grassland sites with contrasting microclimatic conditions along a steep elevational macroclimatic gradient in an Alpine region in Central Europe.ResultsSpecies richness and abundance decreased along the elevational macroclimatic gradient, and both benefitted from warm microclimate. Interactive effects of elevation and microclimate on the abundance were, however, species‐specific, and partly mediated by traits: Warm microclimatic conditions facilitated the occurrence of demanding xerophilic and late‐hatching species, resulting in marked community dissimilarities at mid‐elevations where colder sites harboured only a subset of the species. The latter mainly occurred at low elevations together with long‐winged species. Abundance peaks of non‐xerophilic species were further upslope when microclimate was warm. Intraspecifically, the body sizes and wing lengths of the larger females, but not the males, decreased with elevation akin the community mean, and brown colour morphs were more frequent at sites with warm microclimate.Main ConclusionsOur nuanced results reveal that trait‐dependent responses of species to microclimate play a key role in the assembly and structuring of insect communities along macroclimatic gradients. Since microclimate preferences changed with elevation, we conclude that species temperature niches are narrower than the elevational range suggests and both macro‐ and microclimatic conditions must be considered when predicting species responses to climate change. Microclimatic contrasts among sites at similar elevations enhanced species turnover mediated by moisture preferences and phenology, highlighting the importance of mountains for conservation as climatic refugia where species with diverging niches can persist in proximity.

Depth‐independent phenotypic variation of massive Porites coral color morphs

AbstractAs coral reefs continue to decline due to anthropogenic stressors, community characterizations will reveal both historical selection processes and adaptive potential to environmental change. To address the potential role of color in the distribution and resilience of massive Porites corals, we surveyed the distributions of two dominant color morphs (brown and purple), and a unique intermediate state, across a depth gradient in Guam, Micronesia. We found that brown colonies dominated populations across all depths, and larger colonies had higher rates of partial tissue mortality and active disease lesions. Despite the dominance of brown colonies, both brown and purple color morphs showed a high similarity in susceptibility, as indicated by the colony sizes, the severity of partial tissue mortality, and the prevalence of active disease lesions. This is a non‐intuitive result given the presence of phenotypic plasticity between color morphs, evident by an intermediate, transitionary stage between brown and purple colonies that suggests a functional divergence between one color over the other. The study also revealed the dominance of small colonies at depth, which provides some insight into the ecological impacts that may have shaped Guam's current massive Porites population size structure over the past several decades. With this, we provide foundational insight into the adaptive strategies and historical pressures that have shaped the modern massive Porites population.

Cold winters have morph-specific effects on natal dispersal distance in a wild raptor.

Dispersal is a key process with crucial implications in spatial distribution, density, and genetic structure of species’ populations. Dispersal strategies can vary according to both individual and environmental features, but putative phenotype-by-environment interactions have rarely been accounted for. Melanin-based color polymorphism is a phenotypic trait associated with specific behavioral and physiological profiles and is, therefore, a good candidate trait to study dispersal tactics in different environments. Here, using a 40 years dataset of a population of color polymorphic tawny owls (Strix aluco), we investigated natal dispersal distance of recruiting gray and pheomelanic reddish-brown (hereafter brown) color morphs in relation to post-fledging winter temperature and individual characteristics. Because morphs are differently sensitive to cold winters, we predicted that morphs’ natal dispersal distances vary according to winter conditions. Winter temperature did not affect the proportion of brown (or gray) among recruits. We found that dispersal distances correlate with winter temperature in an opposite manner in the two morphs. Although the gray morph undertakes larger movements in harsher conditions, likely because it copes better with winter severity, the brown morph disperses shorter distances when winters are harsher. We discuss this morph-specific natal dispersal pattern in the context of competition for territories between morphs and in terms of costs and benefits of these alternative strategies. Our results stress the importance of considering the interaction between phenotype and environment to fully disentangle dispersal movement patterns and provide further evidence that climate affects the behavior and local distribution of this species.

Water content in diet affects growth and timing of female first mating, but not coloration, in the admirable grasshopper (Syrbula admirabilis)

AbstractUnderstanding how water limitation affects the performance of herbivorous insects is relevant in a context of worldwide alterations of rainfall regimes due to climate change. Apart from its influence on insect growth and development, water availability has also been considered a cue for color polyphenism in some species. This is the case of the grassland‐inhabiting admirable grasshopper (Syrbula admirabilis), for which water content in plant tissues, a potentially reliable cue to predict future vegetation conditions, has been proposed to determine the frequency of green–brown color morphs. We performed an experiment that manipulated water content of the diet (dry/wet treatment) in a group of individually monitored admirable grasshoppers to explore the effects on imago size, timing of female first mating, and coloration. Our results showed that grasshoppers in the wet treatment achieved larger sizes, and females mated comparatively earlier, than their counterparts in the dry treatment. We also found that hue (the dominant color) in imagines was significantly lower (browner) than in nymphs, but the magnitude of this color shift did not differ between treatments. This study supports the idea that water limitation has a negative impact on grasshopper growth and development, but rules out dietary water content as a cue for color polyphenism. This result encourages additional research to assess the actual contribution of environmental and genetic factors to color determination in admirable grasshoppers. Such information could help to better understand how color polymorphism is maintained in natural populations and to predict how it could evolve in a future in which environmental conditions will become more unpredictable.

A New “Business as Usual” Climate Scenario and the Stress Response of the Caribbean Coral Montastraea cavernosa

The climate change related decline of shallow (<30 m) coral reef ecosystems has been driven by the significant mortality of scleractinian corals caused primarily by the phenomenon known as “coral bleaching”. Despite pervasive phase shifts and macroalgal dominance on many coral reefs some coral species have persisted on many reefs. One of those species is Montastraea cavernosa which has been categorized as resilient to a range of biotic and abiotic insults. Here we present the results of a thermal stress and ocean acidification experiment on M. cavernosa, both its brown and orange color morphs, closely representing predictions from the Representative Concentration Pathway (RCP) 6.0 scenario in the year 2100. We assessed the community response of the microbiome, and the molecular responses of critical pathways in the host by quantifying transcript abundances of genes encoding fluorescent proteins, heat shock proteins, antioxidant enzymes and regulators of apoptosis. After a 12 d acclimatization experiment no visible bleaching was observed in any treatment, and the excitation pressure on photosystem II of the symbiotic Symbiodiniaceae, while lower under the combined effects of thermal stress and ocean acidification, was not significantly different than control samples. Only minor, but significant, changes in the prokaryotic microbiome were observed when exposed to RCP 6.0 predicted ocean acidification conditions. At the end of the experiment, the host heat shock protein 90 (HSP 90) showed an increase in transcript abundance under the interactive effects of thermal stress and ocean acidification compared to high temperatures alone, but these treatment groups were not significantly different than treatments under normal temperatures. While Bax, an activator of apoptosis, was significantly higher under thermal stress alone compared to control samples. Taken together, M. cavernosa, exhibits persistence, resistance and resilience generally, and when experimentally exposed to the more realistic RCP 6.0 climate model conditions.

Behavioral and Morphological Divergence of Sympatric Morphotypes ofLeptopelis flavomaculatus(Anura, Arthroleptidae) in Northeastern Tanzania

Adult males of the African treefrog species Leptopelis flavomaculatus occur in either brown or green color morphs. In this study, we investigated whether the two color morphs of breeding males of L. flavomaculatus differ in traits other than color. We examined call differences (dominant frequencies and call durations), call-site selection, and body size. Our results show differences in the call durations, dominant frequencies, mean call intensities, as well as in size (body length and body mass) of the two vocally active color morphs of this species. The two morphs were similar in their choice of plant species used as calling sites and the heights of those sites. Given the sensitivity of mate recognition systems for most anurans, our results provide evidence of both call and morphological variation between the two color morphs of this species. Our findings establish a foundation for future phylogenetic and mating system studies to support the contention that the two color morphs of L. flavomaculatus might warrant taxonomic recognition as separate species.

Molecular differentiation of epigeic and anceic forms of Drawida ghilarovi Gates, 1969 (Moniligastridae, Clitellata) in the Russian Far East: Sequence data of two mitochondrial genes

Mitochondrial cytochrome oxidase subunit I (COI) and 16S rRNA gene sequence data were analysed for 43 specimens of Drawida ghilarovi – earthworms of a tropical genus on the northern boundary of their natural habitat, including two ecological forms and three colour morphs collected from different regions of the southern Russian Far East. Intraspecific genetic differentiation of these clitellata was analysed with different criteria that characterise different forms and morphs. A sample of anecic worms was shown to possess higher genetic variation than a sample of epigeic worms. Haplotype network reconstructions showed that the meadow-swamp epigeic black-coloured D. ghilarovi is more highly diverged from the anecic forest grey- and brown-coloured worms than the grey and brown colour morphs are from each other. Genetic differentiation between three colour morphs ranged from 9.89 ± 0.58 to 11 ± 0.59% using COI and 16S data. An AMOVA test and an exact test showed a high probability of non-differentiation between grey and brown earthworms. A multimodal mismatch distribution was revealed for the whole D. ghilarovi sample and for each colour morph. The minimum spanning tree showed that the differentiation of specimens is associated with ecological and geographical criteria. Molecular data for Drawida showed high genetic differentiation between epigeic and anecic using COI and 16S gene sequence data as well as the various phylogenetic relationships among the studied forms. The anecic earthworms possibly represent different genetic lineages of the D. ghilarovi species complex. The epigeic Drawida, based on the complex data, can be considered a new species of this genus.

Coral color and depth drive symbiosis ecology of Montipora capitata in Kāne‘ohe Bay, O‘ahu, Hawai‘i

Scleractinian corals form symbioses with diverse photosynthetic dinoflagellates (genus Symbiodinium) that confer varying levels of performance and stress tolerance to their hosts. Variation in thermal stress susceptibility (i.e., bleaching) among conspecific corals is linked to variability in symbiont community composition, yet factors driving heterogeneous symbiont associations within a population are poorly understood. To investigate potential drivers, we characterized Symbiodinium communities in Montipora capitata (N = 707 colonies) across the biophysical regions, reef types, and depth range of Kāne‘ohe Bay (Hawai‘i, USA), where this dominant reef-builder associates with Symbiodinium spp. in clade C (C31) and/or D (S. glynnii), and occurs as brown and orange color morphs. The distribution of these traits was primarily influenced by depth: orange, D-dominated colonies were more prevalent in shallow, high light environments (< 2 m), whereas brown, C-dominated colonies were more prevalent with increasing depth and light attenuation. Though either color morph could be dominated by either symbiont, brown colonies were almost exclusively C-dominated, while orange colonies were more likely to be D-dominated above 4.3 m, and C-dominated below, revealing a significant interaction between color morph and symbiosis ecology. The distribution of orange, D-dominated colonies extended deeper on patch reefs, where light penetrates deeper, compared to the more turbid, fringing reefs, further supporting light as the driver of these patterns. This work reveals that symbiont community variability may arise either from holobiont phenotypic plasticity or differential survival across light gradients, with implications for predicting coral bleaching responses and informing management applications such as selective breeding of robust corals.

Colour change in a filefish (Monacanthus chinensis) faced with the challenge of changing backgrounds

The marine macroalga Caulerpa taxifolia is increasing its distribution worldwide, both within its natural range, where it can replace seagrass following a disturbance, and in areas where it is invasive. C. taxifolia presents a bright green background colouration for inhabitants, while seagrass habitats are typically much deeper green in coloration. The fan-bellied leatherjacket, Monacanthus chinensis inhabits both seagrass Zostera muelleri and C. taxifolia habitats in Moreton Bay, Australia and is camouflaged in these contrasting habitats by brown and bright green colour morphs, respectively. Aquarium experiments measuring colour change of brown and green morphs with respect to contrasting habitats (i.e., brown morphs in C. taxofolia and green morphs in seagrass) revealed that over 21 days, brown morphs significantly altered their skin colouration towards the colouration of green morphs, but green morphs did not alter their colouration. In a habitat preference experiment, brown morphs, which match the colouration of the seagrass, significantly preferred seagrass to C. taxifolia, whilst green morphs showed no preference. We conclude that variations in C. taxifolia coverage present a substantial challenge to this species at short time scales (weeks). This challenge may be overcome by colouration changes at longer timescales assuming fish can survive predation during the adjustment period.

Absence of consistent genetic differentiation among several morphs of Actinia (Actiniaria: Actiniidae) occurring in the Portuguese coast.

Actinia equina, the beadlet sea anemone, is a very labile species, displaying variable colour patterns, broad habitat choice and diverse modes of reproduction. Historically, studies using genetic markers such as allozymes and differences in habitat choice lead several authors to propose that different colour morphs could represent different species. One of the species defined was A. fragacea. In this paper, the relationships between brown, red and green colour morphs of A. equina and A. fragacea were studied, using two DNA fragments (one mitochondrial and one nuclear). Individuals were sampled from three different areas in Portugal separated by a maximum distance of 500 km. This is the first study applying direct sequencing of selected gene fragments to approach the validity of Actinia morphs as different genetic entities. The results show that, at least in the Portuguese coast, these colour morphs do not correspond to the two valid species recognized in the literature. The existence of cryptic species is discussed.

Comparison of the potential rate of population increase of brown and green color morphs of Sitobion avenae (Homoptera: Aphididae) on barley infected and uninfected with Barley yellow dwarf virus

Life tables of brown and green color morphs of the English grain aphid, Sitobion avenae (Fabricius) reared on barley under laboratory conditions at 20 ± 1°C, 65% ± 5% relative humidity and a photoperiod of 16 : 8 h (L : D) were compared. The plants were either: (i) infected with the Barley yellow dwarf virus (BYDV); (ii) not infected with virus but previously infested with aphids; or (iii) healthy barley plants, which were not previously infested with aphids. Generally, both color morphs of S. avenae performed significantly better when fed on BYDV-infected plants than on plants that were virus free but had either not been or had been previously infested with aphids. Furthermore, when fed on BYDV-infected plants, green S. avenae developed significantly faster and had a significantly shorter reproductive period than the brown color morph. There were no significant differences in this respect between the two color morphs of S. avenae when they were reared on virus-free plants that either had been or not been previously infested with aphids. These results indicate that barley infected with BYDV is a more favorable host plant than uninfected barley for both the color morphs of S. avenae tested, particularly the green color morph.

Brown tawny owls moult more flight feathers than grey ones

The mechanisms by which melanin‐based colour polymorphism can evolve and be maintained in wild populations are poorly known. Theory predicts that colour morphs have differential sensitivity to environmental conditions. Recently it has been proposed that colour polymorphism covaries genetically with intrinsic and behavioural properties. Plumage moult is a costly and crucial somatic maintenance function in birds. We used a long‐term data set consisting of 761 observations on 307 individuals captured between 1985 and 2010 to examine differences in partial flight feather moult between grey (pale) and brown (pheomelanic dark) colour morphs of the tawny owl. We find that the brown morph consistently moult more primary flight feathers than the grey morph whereas there is no clear difference between colour morphs in the moulting of secondary feathers. Contrary to expectations, the difference in the number of moulted flight feathers between the morphs was independent of environmental conditions, as quantified by the abundance of prey. We discuss the potential physiological and behavioural causes for and costs of the observed difference in maintenance functions between colour morphs.

Asymmetrical mate preference in recently adapted White Sands and black lava populations of Sceloporus undulatus

Abstract Speciation can proceed rapidly when natural and sexual selection act in concert. For example speciation can be accelerated when traits that confer a selective advantage in a particular habitat also influence mate preference. Studying parallel but evolutionarily independent instances of ecological divergence can illuminate the interaction between natural and sexual selection during speciation. Locally adapted populations of the eastern fence lizard Sceloporus undulatus have recently evolved in three different habitats in the Chihuahuan desert: blanched color morphs occur on the gypsum dunes of White Sands, melanic color morphs occur on the Carrizozo lava flow, and brown color morphs occur in the surrounding desert scrubland. In addition to differences in cryptic dorsal coloration, populations also differ in the size and color of ventral patches used for social signaling. This system therefore provides an opportunity to investigate the interplay of natural and sexual selection during rapid ecological speci-ation. We used mate preference experiments to determine whether locally adapted populations may exhibit the early stages of behavioral reproductive isolation. We observed an asymmetrical mate preference in this system; White Sands males preferentially courted local females, while males from dark soils and black lava populations did not exhibit a preference for local mates. We also found that female behavior and ventral patch phenotype were associated with male courtship. Our results suggest that the observed preference for local mates evolved at White Sands, and we discuss the possible link between local adaptation and traits involved in mate preference in this system.

Cryptic coloration as a predator avoidance strategy in seagrass arrow shrimp colormorphs

The arrow shrimp, Tozeuma carolinense, is a highly abundant small crustacean inhabiting seagrass beds along the US southeastern and Gulf coast. These shrimp inhabit the tops of seagrass blades, feeding on epiphytic algae. Despite T. carolinense abundance, it is largely underrepresented in the diets of predatory fish, presumably due to its cryptic morphology and behavior. Here, we quantify the degree of crypsis of green and brown colormorphs of T. carolinense to the visual systems of two potential predators, dichromatic Cynoscion nebulosus and trichromatic Sciaenops ocellatus, using a visual chromatic contrast model. Contrast of shrimp colormorphs viewed against seagrass backgrounds was similar between predators but varied greatly for both colormorphs among the backgrounds. For both dichromatic and trichromatic predators, green morphs produced significantly less contrast than brown morphs on live seagrass, while brown morphs produced significantly less contrast than green morphs on dead seagrass. Each colormorph had at least one complimentary seagrass species against which it would be difficult for fish predators to discriminate. Model predictions were largely borne out in a survey of a natural population of T. carolinense in Tampa Bay, FL (USA), where shrimp were found only in monospecific patches of live Syringodium filiforme, and green morphs significantly outnumbered brown morphs. Although these shrimp do not rely solely on cryptic coloration for predator evasion, the ability of T. carolinense to match its background does minimize visual contrast and likely contributes to their lack of representation in the diets of predatory fish.

Effects of depth and eutrophication on the zooxanthella clades of Stylophora pistillata from the Gulf of Eilat (Red Sea)

Abstract The symbiotic association between corals and zooxanthellae has been a major contributing factor in the success of reef‐building corals. The diversity of zooxanthellae harboured in the hermatypic coral Stylophora pistillata in the Gulf of Eilat (Aqaba), northern Red Sea, was investigated on the basis of the length and sequence variation of the 18S small subunit ribosomal DNA. Of several clades found worldwide, only clades A and C were found to be associated with this coral species in the Gulf. No correlation between the pink and brown colour morphs of the coral S. pistillata and the zooxanthella clade was found. Shallow‐water colonies (5 m) harbour clade A while deeper‐water colonies (17 m) harbour either clade A or C. This coral is a brooding species that associates with different zooxanthellae at different depths. Eutrophication from fish farms did not affect clade identity associated with Stylophora. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Variation in spectral reflectance of the hermatypic corals, Stylophora pistillata and Pocillopora damicornis

Reflectance spectra were measured off pink and brown color morphs of the branching hermatypic corals Stylophora pistillata and Pocillopora damicornis in the northern Red Sea. Results showed that though some of the brown morphs were identical between coral species, other brown morphs were found only in S. pistillata corals. Reflectance of pink morphs differed between these two species, possibly due to differences in Pocilloporin pigments between them. Spectral variation between color morphs was higher than between species, and corals could exhibit both colors in the same colony. These results show that species recognition based on reflectance spectra is possible in some cases, yet it may be limited to specific color morphs or to discrimination between a small numbers of well-described coral species.

Systematic significance of tridentate pedicellariae in the echinoid genera Diadema and Echinothrix

Abstract. The tridentate pedicellariae in all species of Diadema and Echinothrix recognized by Mortensen, plus species described later (to include D. palmeri and two color morphs of E. calamaris) were examined to identify diagnostic species characters, and to determine whether such characters are useful in inferring phylogenetic relationships between species. Nineteen morphological characters were measured and analyzed, and species‐specific characters were identified. The morphometric data were then transformed using gap coding and a parsimony analysis was undertaken. The resulting cladogram for the tridentate pedicellariae present in species of Diadema was compared with the mitochondrial DNA phylogeny of Lessios et al., with a good level of congruence observed. Very narrow forceps‐like tridentate pedicellariae were found to be basal among Recent species, present only in D. setosum and D. palmeri. Members of D. palmeri were found to be unique within the genus, having both the forceps‐like form and a broad form of tridentate pedicellaria. The very narrow forceps‐like form is absent in all subsequent divergent species, while the broad form of tridentate pedicellaria in D. palmeri is basal to the broad forms in D. antillarum, D. mexicanum, D. paucispinum, and both the broad and narrow forms of tridentate pedicellaria of D. savignyi. The greatest similarity was found between the broad forms of tridentate pedicellaria in D. antillarum and D. mexicanum. These species were also found to have narrow forms of tridentate pedicellaria that showed a reasonable level of association to one another and to the rostrate form in D. ascensionis. Since the work of Mortensen, D. ascensionis has been shown, using mitochondrial DNA, to be nested within D. antillarum. The results of this study show that the tridentate pedicellaria in D. ascensionis are distinctly different from all other forms within the genus, to the extent that they belong to a rostrate subclass. This indicates that, among Diadema species, the tridentate pedicellariae are one of the first morphological characters to diverge in genetically isolated populations. Unlike the tridentate pedicellariae in Diadema, the different forms of tridentate pedicellariae in E. calamaris and E. diadema showed a stronger association intraspecifically than between forms interspecifically. The small forms of tridentate pedicellaria of the white and brown color morphs in E. calamaris showed a high level of association, while the large forms showed only a moderate association, far lower than would be expected between color morphs of the same species. This suggests that they are either subspecies or recently diverged separate species. This study demonstrates the taxonomic value contained within the characters of the tridentate pedicellariae for both differentiating species (even subspecies) and inferring phylogenetic relationships between species.

Lunar periodicities of diadematid echinoids breeding in Fiji

Gonad indices for two species of Diadema and two species of Echinothrix, including two color morphs of Echinothrix calamaris, are described for a 12-month period on Sosoikula Reef and Nukubuco Reef, Viti Levu, Fiji. Seasonal fluctuations in salinity (36.11±0.88 ppt) and water temperature (26.35±0.91°C) occurred. Gonad index data showed monthly reproductive rhythms, closely attuned to the lunar cycle. Diadema savignyi and Echinothrix diadema spawned on the full moon, and Diadema setosum and E. calamaris (white and brown color morphs) spawned on the new moon. Breeding periodicities coincided with the spring tides, thus maximizing chances of fertilization and dispersal. Such breeding cycles indicate how closely related species can co-exist with minimum risk of hybridization. Unusual sex ratios were found for all species, with an exceptionally low incidence of males. Reasons for this deviation from the typically reported 1:1 sex ratio may relate to the exceptionally high levels of tributyltin (TBT) recorded in Suva Harbor.

How do morphotypes and chemotypes relate to genotypes? The colonial ascidian Cystodytes (Polycitoridae)

Intraspecies variability is widespread in marine invertebrates. Size, colour, texture, general shape and secondary chemistry can differ quite drastically from one individual to another. Cystodytes dellechiajei (Polycitoridae) is a cosmopolitan colonial ascidian with several morphotypes, most of which differ in colour and spicular composition. New molecular tools enable us to assess the taxonomic status of these morphotypes. To determine whether variation observed in Mediterranean Cystodytes has a genetic basis, we sequenced 45 specimens from eight locations of the western Mediterranean and one from Mayotte (Indian Ocean), and obtained a 617 bp fragment of the mitochondrial gene COI. Fifteen different colour morphs were recorded and four kinds of spicules were found: disk‐shaped, sphere‐shaped, star‐shaped and discoidal, thick spicules with a toothed margin. Zooid morphology was remarkably uniform in the whole sample set. Different tree construction methods (distance‐based, parsimony‐based, and maximum‐likelihood‐based) yielded consistent results, and recognized six major clades, which had no correspondence with spicule shape and were only partially consistent with colour morphs. Results are discussed in the light of previous knowledge of the chemistry of blue, green, brown and purple colour morphs. In spite of the different colour patterns and spicular variability we concluded, on the basis of chemical and genetic data, that the morphological traits analysed were not consistent enough to be used to differentiate between Cystodytes species. We point out the importance of genetics and chemistry in assessing the taxonomic status of species with variable morphology.

Taxonomic significance of spine morphology in the echinoid genera Diadema and Echinothrix

Abstract. The spine morphology of all established species of Diadema and Echinothrix, including 2 color morphs of E. calamaris, were examined externally and internally via transverse sectioning to identify diagnostic species features and to assess the morphological relationship between species. Forty‐nine different morphological characters were measured and analysed using ordination by multi‐dimensional scaling (MDS) and cluster analysis. Specimens of Diadema paucispinum and D. setosum had very distinct spine structures. In D. paucispinum, the spines were more robust than those of other species of Diadema. This was evident in the spine's internal structure, with large, closely packed solid wedges, a small axial cavity, and rings of trabeculae throughout the spine's length. The spines in D. setosum were distinctive because of their length in relation to test size and the reduced flaring of their verticillations. The spines of other members of this genus were very similar to each other. Without careful sectioning, the spines from specimens of D. antillarum, D. ascensionis, D. mexicanum and D. savignyi were difficult to differentiate. The internal structures of spines for each species did, however, possess a combination of features that differentiated the species. Such features included the shape, orientation, and number of solid wedges, the presence or absence of spokes and rings of trabeculae between the solid wedges, and the presence or absence of tissue within the axial cavity. Individuals of Diadema palmeri also had spines morphologically similar to other species, however, the red pigmentation of these spines (in life and when preserved) made them easily distinguishable. The spine structures of the 2 species of Echinothrix were starkly different, while the white and brown color morphs of E. calamaris had morphologically distinctive ambulacral and interambulacral spines. The blunt, open‐tipped interambulacral spines, with reticular tissue present in the axial cavity of the white color morph, were easily distinguished from the pointed, closed‐tipped spines, with a hollow axial cavity found in the brown color morph. Such differences indicate that the brown color morph is either a subspecies or a separate species. Taken together the data show that each species has significant morphological differences in the structure of the spines. It is evident from our data that spine morphology is a useful tool to differentiate these commonly confused species.