Confirmation of serial spawning in the chokka squid Loligo vulgaris reynaudii off the coast of South Africa

Ovary maturation and spawning in the chokka squid Loligo vulgaris reynaudii were investigated by collecting squid from across their distributional range on the southeastern coast of South Africa between 1992 and 1993. Based on histological examination of the ovarian tissue and the separation of multiple modes in oocyte size-frequency distribution, ovary development was characterised by eight distinct stages. Our study confirms serial spawning in L. v. reynaudii. Received: 9 October 1998 / Accepted: 22 April 1999     

The location of spawning grounds,spawning and schooling behaviour of the squid Loligo vulgaris reynaudii (Cephalopoda: Myopsida) off the Eastern Cape Coast,South Africa

The location of spawning grounds of the squid Loligo vulgaris reynaudii (D'Orbigny) was investigated in the years 1988–1990. At least 39 spawning sites were found during this period along the inshore areas of the Eastern Cape coastline between Algoa Bay and Plettenberg Bay. The substrate chosen for egg laying was mostly fine sand or flat reef, frequently in large and relatively shettered bays. Spawning was found to occur sporadically throughout the year, and some spawning sites were used repeatedly within a particular year and in subsequent years. Squid migrate in discrete schools separated by sex in the vicinity of the spawning sites; these schools mix during spawning. Mating and egg deposition behaviour is described from observations made on the spawning grounds. Cannibalism was seen on a number of occasions, but no post-spawning mortality was recorded. Egg beds consisted mostly of large concentrations of egg strands (>3 m in diameter), with smaller aggregations of one to ten egg strands surrounding these, with single strands in the immediate vicinity. Three basic patterns of echotraces were identified and interpreted according to diving observations. These patterns were classified as loose patches, dense patches, and complex patterns. The first two represent non-spawning schooling patterns and the third, mating and egg laying behaviour. This observation led to the general classification of squid aggregations: schools (non-spawning mode) and concentrations (spawning mode). Concentrations as far as Loligo vulgaris reynaudii was concerned were further divided into two patterns: suprabenthic and benthic (spawning) squid.     

Small-scale spatial and temporal patterns of egg production by the temperate loliginid squid<Emphasis Type="Italic"> Sepioteuthis australis</Emphasis>

This study explored the spawning dynamics of southern calamary (Sepioteuthis australis) by estimating small-scale temporal and spatial variability in egg production in an area known to attract spawning aggregations. Surveys of the seagrass beds (Amphibolis antarctica) over 14 months determined the timing and location of egg deposition, as well as estimating total egg production and loss of deposited egg masses from the spawning grounds. Egg laying in the inshore seagrass beds occurred predominantly during the austral spring and early summer. Egg production at one location (Hazards Bay) was very similar between the two years, but at the second location (Coles Bay) egg production was threefold less during the second summer. There was considerable spatial variability in egg production among seagrass beds within a kilometre of each other as well as within 10 km. Variability in the use of seagrass beds by the squid during each summer could not be attributed to differences in seagrass density or vegetation cover. Losses of deposited egg masses in the A. antarctica beds were detected on two occasions. On the first occasion the loss was correlated with storms; however, the second and smaller loss of egg masses was not correlated with storm activity. Information about the spatial and temporal patterns of egg production was used to make recommendations about the use of fishing closures to protect spawning adults from over-fishing.     

Does egg colour affect predation rate on open passerine nests?

The breeding success of many passerines is strongly reduced by egg predation. The adaptive significance of egg crypsis in open nesters is often taken for granted, but visually searching predators may first detect the nest or adult bird and not the eggs. Götmark predicted that selection should favour egg crypsis in the absence of conspicuous nests, whereas birds with conspicuous nests should have non-cryptic eggs. I compared the effect of egg colour treatment (white, blue, brown-spotted) on nest survival (1) among species characterized by different egg coloration, nest size and nest placement, and (2) between relatively well and poorly concealed nests within species. I used artificial nests (n=1,296) and eggs mimicking (except in egg colour) those of the yellowhammer (Emberiza citrinella), blackcap (Sylvia atricapilla) and song thrush (Turdus philomelos). Concurrently, I monitored survival of real nests (n=1,106). Nest survival differed among species, increased with nest concealment and throughout the breeding season, but was not significantly related to egg colour in any species. Nevertheless, the data for the yellowhammer suggest a trend in survival rates across the colour treatments. Brown eggs survived better than white eggs by 11% and 4% in 2 years, but this study had insufficient power to detect effects of this size. The results thus suggest that egg coloration in the song thrush and blackcap (shrub nesters) may be a neutral trait with regard to nest predation, whereas egg crypsis may be an anti-predation feature for the yellowhammer (ground/near-ground nester). The role of predation in the evolution of eggshell colour may vary not only between cavity and open nesters, but also across nest sites within the latter group.     

Large-scale oceanic distribution and population structure of Calanus finmarchicus, in relation to physical environment, food and predators

The investigation was carried out from 62°N to 73°N and from 14°E to 11°W in the Norwegian Sea during 19 June-12 July 1997. Regional differences in the phase of the seasonal development of the plankton community were evident, most pronounced across the Arctic front. In the Coastal and eastern Atlantic domains, post-bloom conditions prevailed, characterised by low chlorophyll a (chl a) levels and a phytoplankton assemblage dominated by coccolithophorids and small flagellates. During the study period, egg production rates of Calanus finmarchicus were low (<10 eggs female^-1 day^-1), older copepodite stages dominated, and the seasonal descent to deeper waters had started. In the Arctic domain, bloom conditions were evident by high chl a levels and a high abundance of large diatoms. Egg production rates were higher (a maximum of 29 eggs female^-1 day^-1), but the dominance of stages CI-CIII indicated that considerable spawning had already occurred prior to the spring bloom. The seasonal descent had barely started. Both invertebrate and fish predators were most abundant in the Coastal and eastern Atlantic domains, with abundance strongly decreasing north-westwards. No tight relationship between total abundance of invertebrate or fish predators and that of C. finmarchicus was apparent. However, a weak, but significant, relationship between abundance of young stages of chaetognaths and Euchaeta spp. versus young stages of C. finmarchicus was found, indicating that these invertebrate predators develop parallel to the development of the new cohort of C. finmarchicus. In early summer, C. finmarchicus had reached overwintering stages, and had started to accumulate in deeper waters in areas with the highest abundance of horizontally migratory planktivorous fish.     

Foraging, prey capture, and gut contents of the mesopelagic narcomedusa Solmissus spp. (Cnidaria: Hydrozoa)

Narcomedusae are the most common group of medusae in the mesopelagic depths of Monterey Bay, California. Numerous capture events of various prey taxa were recorded in situ and analyzed using the Monterey Bay Aquarium Research Institute's remotely operated vehicle "Ventana". In situ video analysis of the stomach contents of 82 Solmissus incisa and S. marshalli revealed 88 identifiable prey items. Most (88%) were gelatinous animals. Of these gelatinous prey, 60.3% were ctenophores, 20.5% were cnidarians, 12.8% were salps, 3.8% were chaetognaths, and 2.6% were polychaetes. Euphausiids accounted for 11.4% of the diet, but they were probably captured adventitiously, as the gut contents of ctenophore prey. The tentacle-first foraging behavior of the narcomedusae is an effective way to capture large, comparatively fast-moving prey, because the fluid disturbance caused by swimming is decoupled from the area of prey capture. This behavior contrasts with the prevailing models of feeding behavior in medusae. Stealth predation may be the dominant mode of capturing prey by medusae in the mesopelagic depths of the oceans.     

Shark-inflicted injury frequencies, escape ability, and habitat use of green and loggerhead turtles

Interactions between large marine predators and their prey are difficult to observe and little is known about the risk of predation faced by sea turtles. The frequency of predator-inflicted injuries, however, has afforded insights into the predation risk faced by many taxa. We measured the frequency of shark-inflicted injuries on green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtles in Shark Bay, Western Australia with a view to determining differences between species and sex-classes in the risk of predation from tiger sharks (Galeocerdo cuvier). Furthermore, we investigated how escape ability and habitat use might influence the probability of turtles being injured by sharks. Shark-inflicted injuries were more frequent on loggerhead than on green turtles, and most frequent on adult male loggerhead turtles. Species effects could not be attributed to differences in habitat use, since green turtles were found in habitats favored by tiger sharks more often than were loggerhead turtles. Green turtles, however, were faster and maneuvered better than loggerhead turtles, suggesting that escape ability is a factor in interspecific differences in injury frequency. The sex-class difference in injury frequency of loggerhead turtles suggests that males face greater predation risk than females and may take more risks. For green turtles, the lack of a sex difference in injury frequency might be due to greater escape ability lowering overall predation risk or to no differences between sexes in the benefits of risk-taking.     

Anti-predator benefits of group living in white-nosed coatis (Nasua narica)

Predation is often considered an important factor in the evolution of sociality among animals. We studied mortality patterns and grouping behavior of white-nosed coatis (Nasua narica) at sites in southern Arizona, USA, and western Jalisco, México. Coatis were monitored by radio-tracking and recaptures for more than 3 years at each site. In both populations, predation by large felids, including jaguars (Panthera onca) and pumas (Puma concolor), accounted for more than 50% of mortality of adult coatis. Predation rates were significantly higher on solo coatis than on coatis in groups at both study sites. Predation rates were negatively related to group size in Arizona. However, mortality of juveniles, as measured by the ratios of juveniles to adult females, was not related to the number of adult females per group in Arizona or Jalisco. Coatis exhibit a suite of behaviors, including foraging with the juveniles in the center of the group, sharing vigilance, alarm calling, mobbing and attacking predators, and a highly synchronous birth season, that are all consistent with the hypothesis that predation has played an important role in shaping coati social behavior.     

Density affects female and male mate searching in the fiddler crab, <Emphasis Type="Italic">Uca beebei</Emphasis>

In most species, only one sex searches for mates while the other waits. Models of sex-specific mate-searching behavior predict single-sex searching, but the factors that determine which sex searches are not understood. In this study, we examine the effects of density and predation risk on mate-searching behavior in the fiddler crab Uca beebei. U. beebei is one of the few fiddler-crab species in which both sexes search for mates. In a field experiment conducted in Panama, we manipulated crab density and perceived predation risk in replicate plots. Females searched more and males searched less at high densities. At high levels of perceived predation risk, both sexes similarly reduced their search rates. Observations of plots that naturally varied in crab density show that females were more likely to search for mates in areas of higher density, where there were more males. Females may preferentially search for mates in high-density areas because the abundance of nearby burrows, into which they can run to escape predators, decreases their costs of searching and because the abundance of males and male burrows facilitates comparisons and thus may increase their benefits from searching. Males at high densities decrease their mate-searching rate perhaps in response to the increase in female searching and to the corresponding increase in the intensity of their competitors' mate-attraction signals.     

Alarm responses of the green sea urchin, Strongylocentrotus droebachiensis, induced by chemically labelled durophagous predators and simulated acts of predation

The green sea urchin, Strongylocentrotus droebachiensis, exhibited immediate behavioural responses to waterborne chemosensory cues from two durophagous predators, the Atlantic wolffish, Anarhichas lupus, and the edible crab, Cancer pagurus; as well as from crushed conspecifics and crushed blue mussels, Mytilus edulis. The response patterns were dose dependent and diet dependent. Strong responses were elicited by water conditioned by echinivorous wolffish (97.5%), undiluted urchin extract (73%), undiluted mussel extract (52.5%), and by water conditioned by echinivorous crab (45%). In contrast, urchin extract diluted to 1%, mussel extract diluted to 10%, and water conditioned by predators on a mussel diet elicited weak responses (~20%). Infection by the endoparasitic nematode Echinomermella matsi had no significant effect on the response pattern of S. droebachiensis. There was no conclusive evidence of an alarm response to the predators per se, as the weak response to stimuli from non-echinivorous wolffish and crab, as well as from the seastar Asterias rubens, may have been caused by chemical cues transmitted from their mussel diet. The diet-dependent response to predators suggests that active predators were labelled by chemical cues from their echinoid prey. The chemical cue from echinivorous wolffish acted as both an arrestant and as a repellent, whereas the response to other cues was predominantly or exclusively repellent. The response to echinivorous wolffish was quantitatively stronger than, and qualitatively different from, the response to other stimuli, including undiluted urchin extract. The wolffish is apparently being labelled by a latent chemical cue which derives its potency from activation by, or interaction with, substances in the digestive system of the wolffish. We interpret this novel phenomenon as evidence of alarm signal magnification. The induced behavioural modifications demonstrate the green sea urchins' ability to detect chemical cues associated with active durophagous predators, and would therefore seem to have adaptive potential as a predator defence mechanism.     

Foraging behavior of juvenile Carcinus maenas (L.) and Cancer pagurus L.

Information concerning the way juvenile crabs choose their diet from a variety of prey types can be useful for a better understanding of community dynamics, as well as for the adequate management of natural resources. Prey size and species selection by juvenile Carcinus maenas (15-35 mm carapace width, CW) and Cancer pagurus (20-40 mm CW) feeding on four bivalves of contrasting shell morphology were investigated. When offered a wide size range of Mytilus edulis, Ostrea edulis, Crassostrea gigas, and Cerastoderma edule presented individually, crabs generally showed evidence of size-selective predation. Cancer pagurus selected larger mussels relative to the size of their chelae (relative prey size, RPS) than did Carcinus maenas of similar and even larger carapace width. However, the RPS of selected O. edulis and Cerastoderma edule were similar for all crabs, suggesting that certain prey features constitute effective barriers even to the powerful chelae of Cancer pagurus. When offered a wide size range of mussels and oysters simultaneously, all crabs consistently selected mussels. When offered O. edulis and Crassostrea gigas, crabs consumed both these oyster species in similar numbers. Carcinus maenas consumed similar numbers of mussels and cockles; Cancer pagurus, however, showed no preference for either prey in the smaller size classes but selected more mussels than cockles as prey increased in size. Although previous studies report that adult Carcinus maenas select prey species according to their profitability (amount of food ingested per unit of handling time, milligrams per second), consumption rates of the size classes of prey selected by juvenile shore crabs did not always parallel prey value. Although variations in crab strength can account for many of the differences between the foraging strategy of juvenile and adult C. maenas, our results suggest that juvenile crabs are less species selective than adults as a result of the restrictions imposed on small individuals that have limited access to larger prey.     

Optimizing rearing conditions of hatchling loliginid squid

Eggs laid by the California market squid (Loligo opalescens) were collected from spawning grounds and reared in the laboratory. The eggs were maintained in a rearing tank that was part of a closed, recirculating system. The system included seven 220-l circular tanks with attached filtration. Five experiments were conducted to test hatchling survival. One of them evaluated survival on three different food types: (a) enriched Artemia sp. nauplii, (b) wild zooplankton and (c) a mixture of a and b plus mysid shrimp. This mixture of food types (c) was offered to the hatchlings in the other four experiments. High mortality occurred in all experiments between days 1 and 15 post-hatching. However, survival over the entire time span of the experiments (45-60 days) was between 36% and 60%. These survival rates are well above previously reported survival rates for the same time period, and overall are up to 35% better than any survival results ever attained for the routine culture of Loligo spp. squid. Results suggest that high survival can be achieved by: (1) rearing hatchlings in a recirculating system consisting of small round tanks designed to maintain water quality and pH within narrow limits (8.1-8.4), (2) maintaining low current speed (1.0-1.4 cm s^-1) to reduce skin damage and to enhance hatchling-prey interactions, (3) increasing feeding rate by feeding small amounts of food at regular intervals (every 2-3 h) during day time hours and keeping prey densities above 50 prey l^-1, (4) feeding hatchlings with enriched Artemia nauplii during days 1-30 post-hatching and (5) feeding a variety of prey types and sizes to match the different sizes and hunting abilities of same-aged but heterogeneously developing hatchlings. The results from this study will enhance future culturing efforts for the commercially important loliginid squid.     

Reproductive cycles of three dominant Calanus species in Disko Bay, West Greenland

This study describes the annual reproductive cycles of the three dominant Calanus species, C. finmarchicus, C. glacialis and C. hyperboreus, in Disko Bay (West Greenland) in relation to seasonal phytoplankton development. Relative abundance of females, copepodite stage V (CV) and males, and the developmental stage of the female gonad were examined from plankton samples collected at weekly to monthly intervals from May 1996 to June 1997 with a WP2 net or a pump. During spring and summer, egg production rates were determined. Females of all three species were present year round. Maximum relative abundance was reached by C. hyperboreus females at the beginning of February, by C. glacialis in mid-February, and by C. finmarchicus in April. All three species reproduced successfully in Disko Bay. Their reproductive cycles were considerably different with respect to the timing of final gonad maturation and spawning, and hence in their relation to seasonal phytoplankton development. In all three species, early gonad development took place during winter, before living food became plentiful, suggesting that these processes were largely food independent. Final gonad maturation and spawning in C. finmarchicus was related to the phytoplankton concentration, reflecting that final gonad maturation processes are food dependent in this species. C. glacialis females matured and spawned prior to the spring bloom. Our results indicate that first internal lipid stores and later ice alga grazing supplied final gonad maturation and egg production. Maximum egg production rates of C. glacialis were found in spring and summer, when the chlorophyll a concentration was high. Mature female C. hyperboreus were found from February until mid-April, when the chlorophyll a concentration was still low. In this species, reproductive activity was decoupled from phytoplankton development, and final maturation processes and spawning were solely fuelled by internal energy stores.     

The spider and fly revisited: ploy–counterploy behavior in a unique predator–prey system

Earlier studies have shown that the sarcophagid fly Arachnidomyia lindae is the principal egg-sac predator of the colonial orb-weaving spider Metepeira incrassata, and that risk of egg-sac loss increases with group size. Observations of specialized behaviors for attack (flies) and defense (spiders) suggest that this predator-prey relationship may incorporate elements of ploy and counterploy behavior. Here we explore this relationship in detail and test hypotheses regarding efficacy of attack and defense behaviors. Egg-sac guarding by the spider includes defensive behaviors specific to this fly predator, which were observed during experimental "attacks" with tethered A. lindae, but not with similar presentations of non-predatory Musca domestica. Experimental studies also show that Metepeira incrassata recognizes this predatory fly by airborne cues (i.e., the signature frequency of wing-beats), and can distinguish between this predator and other flies (potential prey) on the basis of wing-beat frequency differences. Removal of female spiders results in a significantly higher probability of unguarded egg-sacs being parasitized, demonstrating the adaptive value of spider defensive behaviors. We also present evidence that A. lindae utilizes a behavioral ploy for circumventing spider guarding behavior (aggressive mimicry - producing vibrations of captured prey in the web), and that Metepeira incrassata, in turn, exhibits a counter-ploy behavior (signal thread cutting) to eliminate this potentially distracting vibratory information. While previous studies have shown that this colonial web-building spider uses a number of general attack-abatement mechanisms against a diversity of predators and parasitoids, results of this study suggest that selection pressures from a highly specialized predator may also result in evolution of predator-specific prey responses.     

Balancing between mutualism and exploitation: the symbiotic interaction between Lasius ants and aphids

Nests of Lasius niger (L.) ants were given varied food regimens to test whether their behaviour towards an aphid partner, Aphis fabae (Scop.), changed with alternative food supplies. Honeydew collection and predation on aphids were measured by video monitoring the movement of ants between their nest and an aphid aggregation. Data collected from the aphid aggregations enabled comparisons between remaining aphid biomass and between the tending intensities of the ants. I tested how ant behaviour was influenced by their access to alternative prey and sugar. The results showed that ants accepted a honey solution as a substitute for the honeydew produced by aphids. Ants not only attended their aphid partners, but also preyed on them. The average predation rate increased eightfold when ants were offered the alternative of sugar, whereas alternative prey had no significant effect. In contrast, ant-tending intensity decreased with alternative sugar whereas alternative prey elicited no effect.     

Reproductive biology in two species of deep-sea squids

Deep-sea squids, Moroteuthis ingens and Gonatus antarcticus, were collected in the slope waters off the Falkland Islands and their reproductive systems preserved and investigated onshore. Changes in oocyte length-frequencies at maturation and spawning, and their fecundity were studied. These squids, as well as many other species, are characterised by a synchronous oocyte growth and ovulation. Oviducts are not used for ripe egg accumulation and consequently the universal scale of Lipinski (1979) cannot be applied to assign female maturity. M. ingens spawns near the bottom; its fecundity is 168–297 thousand eggs. Maximum egg size is 1.8–2.7 mm. G. antarcticus spawns midwater; its fecundity is 10–25 thousand eggs. Egg size is 3.2–3.3 mm. In M. ingens spawning takes place in the austral autumn and winter, in G. antarcticus—in austral winter. Our data and the literature data show that the so-called “synchronous ovulation” probably occurs in all deepwater squids. This pattern is very rare among fish, but is quite common among benthic octopods that brood their egg masses.     

Seasonal and sex-specific variations in levels of photo-protecting mycosporine-like amino acids (MAAs) in soft corals

This study focusses on the nature and extent of variation in mycosporine-like amino acids (MAAs) in relation to annual cycles in solar radiation, seawater temperature, and reproduction in reef-flat populations of two soft coral species. The results show MAA tissue concentrations in shallow water colonies of Lobophytum compactum and Sinularia flexibilis to be significantly correlated to annual cycles in solar radiation (P<0.0006 and P<0.0005, respectively) and seawater temperature (P<0.0006 and P<0.0004, respectively). Evidence of seasonal cycles in MAA levels in the tissues of shallow-reef invertebrates positively correlating with annual cycles in solar radiation and temperature suggests that they are an integral component of the soft corals' biochemical defence system against high irradiance and/or temperature stress and thus bleaching. This is further corroborated by the higher production of MAAs in females than males prior to spawning (up to 67% and 56% for L. compactum and S. flexibilis, respectively), presumably to provide a high level of protection against irradiance stress for progeny.     

Blue eggs do not reduce nest predation in the song thrush,Turdus philomelos

Summary Many passerine birds with open cup-shaped nests lay blue or blue-green eggs. In thrushes, blue eggs may be cryptic and provide camouflage by imitating spots of light on green leaves. Alternatively, egg coloration may be selectively neutral because nest predators detect nests and not eggs, or it may be maladaptive because organisms are not always well adapted to their present environment. I evaluated these hypotheses by studying predation on artificial song thrush (Turdus philomelos) nests with quail eggs, painted either white, blue, or spotted (cryptic to a human eye). Corvids were the major nest predators. For concealed as well as exposed nests, I found no differences in the predation rates of nests with white, blue, or spotted eggs. Predators apparently detected the nests, and not the eggs, first. In a second experiment, I placed egg groups without nests in trees to study the effect of color per se. The predation rate of the spotted egg groups was significantly lower than that of the white and blue egg groups, for concealed as well as exposed egg groups. These results suggest that blue eggs in the song thrush are not cryptic but may be selectively neutral or even maladaptive with regard to nest predation.     

Predator hunting mode and habitat domain alter nonconsumptive effects in predator-prey interactions

Predators can affect prey populations through changes in traits that reduce predation risk. These trait changes (nonconsumptive effects, NCEs) can be energetically costly and cause reduced prey activity, growth, fecundity, and survival. The strength of nonconsumptive effects may vary with two functional characteristics of predators: hunting mode (actively hunting, sit-and-pursue, sit-and-wait) and habitat domain (the ability to pursue prey via relocation in space; can be narrow or broad). Specifically, cues from fairly stationary sit-and-wait and sit-and-pursue predators should be more indicative of imminent predation risk, and thereby evoke stronger NCEs, compared to cues from widely ranging actively hunting predators. Using a meta-analysis of 193 published papers, we found that cues from sit-and-pursue predators evoked stronger NCEs than cues from actively hunting predators. Predator habitat domain was less indicative of NCE strength, perhaps because habitat domain provides less reliable information regarding imminent risk to prey than does predator hunting mode. Given the importance of NCEs in determining the dynamics of prey communities, our findings suggest that predator characteristics may be used to predict how changing predator communities translate into changes in prey. Such knowledge may prove particularly useful given rates of local predator change due to habitat fragmentation and the introduction of novel predators.     

Molecular genetic evidence for probable reticulate speciation in the coral genus Madracis from a Caribbean fringing reef slope

For many corals, the existence of morphologically distinct yet sympatric populations/species implies reproductive isolation. Conversely, the presence of many intermediate and overlapping morphologies combined with synchronous, mass spawning suggests incomplete reproductive isolation. In Madracis (Scleractinia: Astrocoeniina: Pocilloporidae), high levels of morphological plasticity among the five most commonly recognized species (M. mirabilis, M. senaria, M. decactis, M. formosa and M. pharensis) on Caribbean reefs led us to question species boundaries. Phylogenetic relationships were investigated at the intra-individual, inter-individual and inter-specific levels using the ITS1-5.8S-ITS2 region (ca. 613 bp) of the ribosomal DNA cistron. Inter-specific divergence was ca. 6%, while intra-individual and intra-specific divergences ranged from 0% to 4.9% and 3.3% to 3.5%, respectively. M. senaria and M. mirabilis formed monophyletic groups. M. formosa, M. decactis and M. pharensis formed a paraphyletic complex. High levels of intra-individual and intra-specific ITS polymorphism in the decactis-formosa-pharensis cluster may be the result of very recent speciation within the clade (i.e. maintenance of ancestral polymorphism and incomplete lineage sorting), or the result of repeated introgressive hybridization among the three taxa. Polymorphism parsimony of 89 sites, including nine that showed additivity, revealed a phylogenetic topology more consistent with inter-taxal hybridization. Results are discussed in terms of weak reproductive barriers, and phylogenetic fission and fusion under Veron's model of reticulate speciation in corals. Ecological studies involving Madracis should consider M. decactis, M. formosa and M. pharensis as a complex.