Distribution of behaviours and species interactions within home range contours in five Caribbean reef fish species (Family Labridae)

Synopsis This study investigated the distribution of behaviours and species interactions within home range contours in five Caribbean labrid species: Halichoeres bivittatus, H. garnoti, H. maculipinna, H. poeyi, and Thalassoma bifasciatum. For this study, contours were defined as: (a) 30%—the core use area, (b) 30–75%—the intermediate activity area, and (c) 75–95%—the peripheral activity area. Behaviours analyzed for this study included: (i) feeding (=biting the substrate or chewing), (ii) chased by pomacentrids, (iii) swimming alone, (iv) swimming with other fishes, and (v) all activities with other fishes. Fifty-nine percent of Halichoeres bivittatus observed showed a higher frequency than expected being chased by pomacentrids in the peripheral region of their home ranges. Halichoeres garnoti showed a lower frequency than expected swimming with other individuals in their core use area, and 64% of the individuals observed showed a higher frequency than expected being chased by pomacentrids in the peripheral region. In general, H. maculipinna exhibited a random distribution of behaviours throughout their home range areas, with a non-significant trend for more agonistic interactions with pomacentrids in peripheral regions. Halichoeres poeyi and T. bifasciatum showed higher frequencies than expected being chased by pomacentrids in the peripheral regions. Overall, the non-random distribution of agonistic interactions with pomacentrids throughout home range areas suggests that the presence or prior residence of territorial pomacentrids on coral reefs may modify the post-settlement selection of home range areas by these labrid species.     

Behavioural Overlap in Six Caribbean Labrid Species: Intra- and Interspecific Similarities

This study investigates behavioural similarities in six ecologically and morphologically similar labrid species. Ontogenetic shifts in behaviour within species are also considered. There have been many studies on ontogenetic differences in fishes with respect to diet, microhabitat use, and visual acuity and how it pertains to foraging ability; however, fewer studies have been specifically directed towards the ontogeny of behaviours. In this study, detailed behavioural observations were recorded of randomly chosen juveniles, initial phase, and terminal phase adults from each of the following species: Halichoeres bivittatus, H. garnoti, H. maculipinna, H. poeyi, and Thalassoma bifasciatum. Only juvenile H. radiatus were observed. The observation periods lasted 10min, and four periods per individual were pooled for analysis. There were many similarities and few striking differences in the behavioural profiles of the six species [discriminant function analysis (DFA) of behaviours correctly classified 60% of the individuals]. In some cases, life intervals within a species separated more strongly than heterospecifics of the same life interval. For example, H. bivittatus juveniles were more similar to H. maculipinna juveniles than to conspecific initial phase and terminal phase adults. From DFA, species were separated in the first discriminant function by an inverse relationship between the frequency of hiding (= out of view) and eating, and life intervals were separated in the second discriminant function by an inverse relationship between the frequency of swimming alone and eye flickering (= remaining motionless and twitching their eyes). Eye flickering is assumed to be a behaviour that increases an individual's awareness of predators or environmental threats. Notable differences among species included the greater frequencies of hiding by juvenile H. radiatus, and all life intervals of H. garnoti. As these labrids grow, they increase their frequencies of swimming alone, and decrease their frequencies of hovering and searching for food. There was a remarkable similarity in ontogenetic changes in these behaviours for all of the species studied.     

Benefits of heterospecific foraging by the Caribbean wrasse,Halichoeres garnoti (Pisces: Labridae)

Synopsis Terminal-phase yellowhead wrasses, Halichoeres garnoti, foraged alone or in association with foraging goatfish, Pseudupeneus maculatus and Mulloides martinicus. Whereas H. garnoti did not dig for benthic infauna, the goatfish foraged almost exclusively on and in sand substrata. Wrasses in the company of goatfish made significantly more strikes on sand substrata than did solitary wrasses, although there were no significant differences in the frequency of strikes on sand and hard substrata combined. The frequencies of other behaviors (searches, scratches, flights, chases, rests, yawns, and cleanings) were not significantly different between solitary and associated wrasses. H. garnoti are attracted to foraging goatfish, which provide access to an otherwise unavailable food resource. To whom reprint requests should be sent     

The effect of territorial damselfish (family Pomacentridae) on the space use and behaviour of the coral reef fish, Halichoeres bivittatus (Bloch, 1791) (family Labridae)

Most demersal species of damselfish (family Pomacentridae) are territorial herbivores that aggressively chase other fishes away from their nests. This study investigates whether the aggressive territorial damselfish, Stegastes leucostictus, modifies behaviours and home range area use in a less aggressive, non-territorial species, the slippery dick wrasse, Halichoeres bivittatus (family Labridae). Damselfishes and wrasses are ubiquitous and abundant members of coral reef fish assemblages around the world; hence, this study has broader implications beyond the two Caribbean species chosen for this study. A manipulative field experiment consisted of transplanting one or three S. leucostictus into artificial shelters positioned within adult or adjacent to juvenile H. bivittatus home ranges. The introduction of damselfish had little effect on the size of home range areas of juvenile or adult wrasses, but had a significant effect on the location of their home ranges. The damselfish also affected adult microhabitat use but did not affect use by juveniles. In addition, there was an increase in damselfish-wrasse interactions that resulted in a significant reduction in the amount of time adult wrasses could spend foraging or in a foraging assemblage. It was concluded that aggressive interactions with territorial damselfish affect individual H. bivittatus space use and may consequently affect the spatial distribution of H. bivittatus populations.     

Hybrids in divers (Gaviiformes)

The incidence of hybridisation in birds differs greatly between orders and is expected to be low in orders comprising few species. The divers or loons (Gaviiformes) are a species-poor group in which apparent hybridisation has been reported infrequently. Here we report on a hybrid diver stored in the collections of the Zoological Museum Amsterdam. The bird shows a heterogeneous set of characters, some shared with the putative parent species White-billed Diver Gavia adamsii and Great Northern Diver G. immer, others being intermediate between the two. A Canonical Discriminant Function analysis positions the bird between these two putative parent species, making a hybrid status quite likely. We evaluate the evidence for hybridisation in the order Gaviiformes and conclude that hybridisation has been suspected in four of the five species, though documentation is limited. If this high incidence could be confirmed, it would rank among the highest of any avian order, contradicting the assumption that incidence of hybridisation in small orders is relatively low.     

Morphological and molecular characterization of a natural hybrid betweenOrchis laxiflora andO. morio (Orchidaceae)

A putative natural hybrid betweenOrchis laxiflora andO. morio (Orchidaceae) from southern Italy, formerly known asO. alata, was characterized both on morphological and molecular grounds in order to confirm its hybrid status and to trace its maternal lineage. The morphological characters of the putative hybrid showed intermediacy between those of the parent species, and restriction fragment length polymorphism (RFLP) analysis of a region of the nuclear ribosomal DNA confirmed its hybrid origin. Chloroplast DNA RFLP analysis indicated thatO. morio provided the maternal genome.     

Confirmation of natural hybrids between Gentiana straminea and G. siphonantha (Gentianaceae) based on molecular evidence

A few individuals with intermediate morphology always appeared in the sympatric distributions of Gentiana straminea and G. siphonantha. These intermediate individuals were hypothesized to be the hybrids of two species after a careful evaluation of their morphological characteristics. To test this hypothesis, sequence comparison of the internal transcribed spacer (ITS) regions of the nuclear ribosomal and trnS (GCU)-trnG (UCC) intergenic spacer region of the chloroplast DNA from Gentiana straminea, G. siphonantha and the putative hybrids was performed. The results suggest that most intermediate individuals were the natural hybrids between G. straminea and G. siphonantha. In addition, we examined the sequence variation among the individuals of both parent species and analyzed the possibility leading to the incongruent identification in some individuals based on morphologic and molecular evidences, respectively. The intraspecific diversification of DNA fragments within both parent species and their high variability in hybrid swarms probably resulted from chloroplast genome recombination and incomplete lineage sorting during the early stages of speciation origin of the parent species. __________ Translated from Acta Botanica Yunnanica, 2007, 29 (1): 91–97 [译自:云南植物研究]     

Natural hybridization origin of <Emphasis Type="Italic">Rhododendron agastum </Emphasis>(Ericaceae) in Yunnan,China: inferred from morphological and molecular evidence

The natural hybridization that occurs between two sympatric species of Rhododendron subgenus Hymenanthes in Yunnan, China, was investigated. The assumed parents, Rhododendron delavayi Franch. and R. decorum Franch., are morphologically distinct, and the putative hybrid species, R. agastum Balf. f. et W. W. Smith, has an intermediate morphology. We used the main morphological characters, sequences of the nuclear ribosomal DNA ITS region, and the chloroplast DNA trnL-F intronspacer to analyze the three species, and compared these morphological and molecular data with an artificial hybrid between R. decorum (♀) × R. delavayi (♂). From the results, we conclude that R. agastum is a natural hybrid between a female R. delavayi and a male R. decorum.     

A comparison of pectoral fin ray morphology and its impact on fin ray flexural stiffness in labriform swimmers

The organization of tissues in appendages often affects their mechanical properties and function. In the fish family Labridae, swimming behavior is associated with pectoral fin flexural stiffness and morphology, where fins range on a continuum from stiff to relatively flexible fins. Across this diversity, pectoral fin flexural stiffness decreases exponentially along the length of any given fin ray, and ray stiffness decreases along the chord of the fin from the leading to trailing edge. In this study, we examine the morphological properties of fin rays, including the effective modulus in bending (E), second moment of area (I), segmentation, and branching patterns, and their impact on fin ray stiffness. We quantify intrinsic pectoral fin ray stiffness in similarly sized fins of two closely related species that employ fins of divergent mechanics, the flapping Gomphosus varius and the rowing Halichoeres bivittatus. While segmentation patterns and E were similar between species, measurements of I and the number of fin ray branch nodes were greater in G. varius than in H. bivittatus. A multiple regression model found that of these variables, I was always significantly correlated with fin ray flexural stiffness and that variation in I always explained the majority of the variation in flexural stiffness. Thus, while most of the morphological variables quantified in this study correlate with fin ray flexural stiffness, second moment of area is the greatest factor contributing to variation in flexural stiffness. Further, interspecific variation in fin ray branching pattern could be used as a means of tuning the effective stiffness of the fin webbing to differences in swimming behavior and hydrodynamics. The comparison of these results to other systems begins to unveil fundamental morphological features of biological beams and yields insight into the role of mechanical properties in fin deformation for aquatic locomotion.     

Genetic admixture despite ecological segregation in a North African sparrow hybrid zone (Aves,Passeriformes, Passer domesticus × Passer hispaniolensis)

Under different environmental conditions, hybridization between the same species might result in different patterns of genetic admixture. Particularly, species pairs with large distribution ranges and long evolutionary history may have experienced several independent hybridization events over time in different zones of overlap. In birds, the diverse hybrid populations of the house sparrow (Passer domesticus) and the Spanish sparrow (Passer hispaniolensis) provide a striking example. Throughout their range of sympatry, these two species do not regularly interbreed; however, a stabilized hybrid form (Passer italiae) exists on the Italian Peninsula and on several Mediterranean islands. The spatial distribution pattern on the Eurasian continent strongly contrasts the situation in North Africa, where house sparrows and Spanish sparrows occur in close vicinity of phenotypically intermediate populations across a broad mosaic hybrid zone. In this study, we investigate patterns of divergence and admixture among the two parental species, stabilized and nonstabilized hybrid populations in Italy and Algeria based on a mitochondrial marker, a sex chromosomal marker, and 12 microsatellite loci. In Algeria, despite strong spatial and temporal separation of urban early‐breeding house sparrows and hybrids and rural late‐breeding Spanish sparrows, we found strong genetic admixture of mitochondrial and nuclear markers across all study populations and phenotypes. That pattern of admixture in the North African hybrid zone is strikingly different from i) the Iberian area of sympatry where we observed only weak asymmetrical introgression of Spanish sparrow nuclear alleles into local house sparrow populations and ii) the very homogenous Italian sparrow population where the mitogenome of one parent (P. domesticus) and the Z‐chromosomal marker of the other parent (P. hispaniolensis) are fixed. The North African sparrow hybrids provide a further example of enhanced hybridization along with recent urbanization and anthropogenic land‐use changes in a mosaic landscape.     

A new natural allotriploid,Lycoris × hubeiensis hybr. nov. (Amaryllidaceae), identified by morphological,karyological and molecular data

A new natural hybrid, Lycoris × hubeiensis K. Liu, is confirmed and described based on morphological, karyological and molecular data. The new natural hybrid displays remarkable morphological differences relative to the putative parents L. radiata (2n = 22 = 22A) and L. aurea (2n = 14 = 8m + 6T), and has a karyotype of 3n = 29 = 4m + 22A + 3T. Two chloroplast intergenic regions of ndhF‐rpl32R and rpl32F‐trnL were sequenced with three haplotypes found in the three taxa. The putative hybrid and L. radiata shared the same haplotype (H1), while L. aurea had two other haplotypes (H2 and H3). Combined with the morphological, karyological and molecular data, we conclude that the hybrid is an allotriploid with L. radiata being the maternal parent offering an unreduced gamete and L. aurea being the male parent.     

Wild hybrids of Lesser White-fronted Goose (Anser erythropus)×Greater White-fronted Goose (A. albifrons) (Aves: Anseriformes) from the European migratory flyway

The Lesser White-fronted Goose [Anser erythropus (Linnaeus, 1758)] is one of the most threatened Palearctic goose species, with the Fennoscandinavian subpopulation in particular having seen a drastic decline over the last century. In the 1990s, captive-bred Lesser White-fronted Geese were used successfully for reintroduction and restocking in Sweden and Finland. The discovery of Greater White-fronted Goose [Anser albifrons (Scopoli, 1769)] mtDNA haplotypes in some of these captive-bred birds (Ruokonen et al. 2000) suggested that hybridisation had occurred during captive propagation and led to the discontinuation of the release of captive goslings. Here we report two hybrids of Lesser×Greater White-fronted Geese that were collected on their wintering grounds in England in 1936 and Holland in 1966. Birds from western Russia normally do not migrate south to Western Europe. Hence, these birds most likely originated from the Fennoscandinavian subpopulation and were collected prior to the commencement of the captive-breeding programmes. Both specimens show a heterogeneous set of morphological characters, some of which shared with the putative parent species and others being intermediate between the two White-fronted Goose species. A Canonical Discriminant Function analysis positions both specimens between the two putative parent species, making their hybrid status likely. We show, thus, that hybridisation between Greater and Lesser White-fronted Geese does occur naturally, albeit perhaps infrequently, and argue that the presence of Greater White-fronted Goose mtDNA haplotypes in Lesser White-fronted Goose may be the result of this naturally occurring hybridisation. Our data provide additional information on the debate whether the restocking programmes were halted for the right reasons and whether it is desirable to re-commence with the reintroduction programme.     

Reticulate hybridization of <Emphasis Type="Italic">Alpinia</Emphasis> (Zingiberaceae) in Taiwan

Reticulate hybridization is a complicated and creative mechanism in plant evolution that can cause interference in phylogenetic studies. Based on observations of intermediate morphology, low pollen fertility, and overlapping distributions of putative parent species, Yang and Wang (Proceedings of the cross-strait symposium on floristic diversity and conservation. National Museum of Natural Science, Taichung, Taiwan, pp 183–197, 1998) first proposed reticulate hybridization of Alpinia in Taiwan. In the present study, molecular tools were used to explore relationships between four parental species and their homoploidy hybrids, and the impact of hybridization on phylogeny reconstruction. Based on DNA markers, maternal heritance of the chloroplast genome, and additivity of nuclear ribosomal internal transcribed spacer, the present results provide strong support for the hybridization hypothesis. Co-existence of parental ribotypes within hybrids revealed that these hybridization events were current, while reciprocal and introgressive hybridization were inferred from chloroplast DNA data. Furthermore, iterative hybridizations involving more than two parental species may occur in notorious hybrid zones. Ecological, phenological, and physiological evidence provides insight into why such frequent hybridization occurs in Taiwanese Alpinia. In the phylogenetic tree of the Zerumbet clade reconstructed in this study, the chloroplast sequences from one hybrid species were not grouped into a subclade, implying instability caused by hybridization. Failure to find morphological apomorphies and biogeographical patterns in this clade was likely partially due to reticulate hybridization. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Natural hybridization of two mussel species <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas, 1771) and <Emphasis Type="Italic">Dreissena bugensis</Emphasis> (Andrusov, 1897)

Dreissenids display a high diversity of shell morphology, and it is frequently difficult to ascribe some individuals from mixed populations to one of the two species, Dreissena polymorpha (Pallas, 1771) or D. bugensis (Andrusov, 1897). Presumably, such individuals may be interspecific hybrids. We have analyzed species-specific allozyme loci of the typical representatives of these two mussel species and putative interspecific hybrids. A natural interspecific hybrid between D. polymorpha and D. bugensis was discovered for the first time by genetic methods. It has been demonstrated that D. bugensis was a maternal parent.     

Molecular evidence for double maternal origins of the diploid hybrid Hippophae goniocarpa (Elaeagnaceae)

Homoploid hybrid plant species are rare, and the mechanisms of their speciation are largely unknown, especially for homoploid hybrid tree species. Two contrasting hypotheses have been proposed to explain the origin of Hippophae goniocarpa: (1) it is a diploid hybrid originating from H. rhamnoides ssp. sinensis × H. neurocarpa ssp. neurocarpa, and (2) it originated via marginal differentiation from H. rhamnoides ssp. sinensis. Regardless of which of these hypotheses is true (if either), previous studies have suggested that H. rhamnoides ssp. sinensis is the only maternal donor for this hybrid species. In this study, we aim to elucidate the maternal composition of H. goniocarpa and to test the two hypotheses. For this purpose, we sequenced the maternal chloroplast DNA trnL‐F region of 75 individuals representing H. goniocarpa, H. rhamnoides ssp. sinensis, and H. neurocarpa ssp. neurocarpa in two co‐occurring sites of the taxa. Seven haplotypes were identified from three taxonomic units, and their phylogenetic relationships were further constructed by means of maximum parsimony, maximum likelihood, and network analyses. These seven haplotypes clustered into two distinct, highly divergent lineages. Two haplotypes from one lineage were found in H. rhamnoides ssp. sinensis, and five (representing the other lineage) in H. neurocarpa ssp. neurocarpa. Hippophae goniocarpa shared four common haplotypes from both lineages, but the haplotypes detected from the two populations differed to some extent, and in each case were identical to local haplotypes of the putative parental species. Thus, both H. rhamnoides ssp. sinensis and H. neurocarpa ssp. neurocarpa appear to have together contributed to the maternal establishment of H. goniocarpa. These results clearly demonstrate that the marginal origin hypothesis should be rejected, and support the hybrid origin hypothesis. Hippophae goniocarpa exhibits a sympatric distribution with its two parent species, without occupying new niches or displaying complete ecological isolation. However, this species has effectively developed reproductive isolation from its sympatric parent species. Our preliminary results suggest that H. goniocarpa may provide a useful model system for studying diploid hybrid speciation in trees. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 156 , 111–118.     

Hybridization of reef fishes at the Indo-Pacific biogeographic barrier: a case study

Hybridization is recognized as an important source of genetic variation. In some reef fishes, including the Acanthuridae, hybridization has been detected due to intermediate colouration. This study used a molecular genetic approach to investigate hybridization in two Acanthurid species: Acanthurus leucosternon and Acanthurus nigricans, which have Indian and Pacific Ocean distributions respectively and are sympatric in the eastern Indian Ocean. In this area a putatitve hybrid, Acanthurus cf. leucosternon has been recognized based on intermediate colouration and restriction to the sympatric region of otherwise allopatric putative parental species. This study aimed to test this hypothesis using genetic tools. The three species were sampled from Cocos (Keeling) and Christmas Islands, the biogeographic boundary where many Indian and Pacific Ocean biota meet. Representatives from allopatric populations of both parental species and outgroups were also sampled. Mitochondrial COI and intron 1 of the nuclear ribosomal protein S7 were sequenced from 13 and 30 specimens respectively. Although sample sizes in this study are relatively small and more genetic data, including an extended phylogeographic sampling, is required to further evaluate these findings, the COI results support hybrid origins of Acanthurus cf. leucosternon, but S7 data are inconclusive due to the possibility of incomplete lineage sorting. The fourfold more abundant Acanthurus nigricans is most often the maternal parent. Inter-fertile hybrids apparently backcross with rare Acanthurus leucosternon males, transferring Acanthurus nigricans mitochondria to this species. These results suggest that Acanthurus leucosternon may eventually be lost from these islands, due to their relative rarity and introgressive hybridization.     

Hybrid origin of Audubon's warbler

Several animal species have recently been shown to have hybrid origins, but no avian examples have been documented with molecular evidence. We investigate whether the Audubon’s warbler (Dendroica auduboni), one of four visually distinct species in the yellow‐rumped warbler complex, has originated through hybridization between two other species in this group, the myrtle warbler (D. coronata) and black‐fronted warbler (D. nigrifrons). Analysis of nuclear amplified fragment length polymorphism (AFLP) and sequence markers shows that Audubon’s warblers are genetically intermediate and carry a mixture of alleles otherwise found only in one or the other of their putative parental species. Audubon’s warblers also carry two deeply divergent mitochondrial DNA lineages, each shared with only one putative parental form. Broad clines between Audubon’s and black‐fronted warblers in AFLP markers call into question the validity of these two forms as full species; nevertheless, our results suggest that the Audubon’s warbler probably originated through hybridization between two long‐diverged species. It is likely that more cases of avian species of hybrid origin will be revealed by surveys of variation in nuclear DNA and other traits.     

Detecting an elusive invasive species: a diagnostic PCR to detect Burmese python in Florida waters and an assessment of persistence of environmental DNA

Recent studies have demonstrated that detection of environmental DNA (eDNA) from aquatic vertebrates in water bodies is possible. The Burmese python, Python bivittatus, is a semi‐aquatic, invasive species in Florida where its elusive nature and cryptic coloration make its detection difficult. Our goal was to develop a diagnostic PCR to detect P. bivittatus from water‐borne eDNA, which could assist managers in monitoring this invasive species. First, we used captive P. bivittatus to determine whether reptilian DNA could be isolated and amplified from water samples. We also evaluated the efficacy of two DNA isolation methods and two DNA extraction kits commonly used in eDNA preparation. A fragment of the mitochondrial cytochrome b gene from P. bivittatus was detected in all water samples isolated with the sodium acetate precipitate and the QIAamp DNA Micro Kit. Next, we designed P. bivittatus‐specific primers and assessed the degradation rate of eDNA in water. Our primers did not amplify DNA from closely related species, and we found that P. bivittatus DNA was consistently detectable up to 96 h. Finally, we sampled water from six field sites in south Florida. Samples from five sites, where P. bivittatus has been observed, tested positive for eDNA. The final site was negative and had no prior documented evidence of P. bivittatus. This study shows P. bivittatus eDNA can be isolated from water samples; thus, this method is a new and promising technique for the management of invasive reptiles.     

Production and cytogenetics of intergeneric hybrids between Brassica napus and Orychophragmus violaceus

The intergeneric hybrid between Brassica napus and Orychophragmus violaceus was obtained by means of embryo culture technique with the latter as the pollen parent. The hybrid was morphologically intermediate between its parents, but could produce a lot of seeds when selfed. Somatic separation of the genomes from the two parental species was observed during the mitotic divisions of some of the hybrid cells. Thus, the hybrid became the mixoploid in nature, consisting of haploid and diploid cells of B. napus, and a nuclear — cytoplasmic hybrid, with the cytoplasm of B. napus and the nuclei of O. violaceus, and the hybrid cells. Pollen mother cells with 19, 12 and 6 bivalents, respectively, were produced by the hybrid. From the selfed progeny of the hybrid, mainly two kinds of plants, B. napus and the hybrid, were found. The hybrid plants of the selfed progeny again produced two kinds of plants, B. napus and the hybrid.     

Hierarchical behaviour,habitat use and species size differences shape evolutionary outcomes of hybridization in a coral reef fish

Hybridization is an important evolutionary process, with ecological and behavioural factors influencing gene exchange between hybrids and parent species. Patterns of hybridization in anemonefishes may result from living in highly specialized habitats and breeding status regulated by size‐based hierarchal social groups. Here, morphological, ecological and genetic analyses in Kimbe Bay, Papua New Guinea, examine the hybrid status of Amphiprion leucokranos, a nominal species and presumed hybrid between Amphiprion sandaracinos and Amphiprion chrysopterus. We test the hypothesis that habitat use and relative size differences of the parent species and hybrids determine the patterns of gene exchange. There is strong evidence that A. leucokranos is a hybrid of smaller A. sandaracinos and larger A. chrysopterus, where A. chrysopterus is exclusively the mother to each hybrid, based on mtDNA cytochrome b and multiple nDNA microsatellite loci. Overlap in habitat, depth and host anemone use was found, with hybrids intermediate to parents and cohabitation in over 25% of anemones sampled. Hybrids, intermediate in body size, colour and pattern, were classified 55% of the time as morphologically first‐generation hybrids relative to parents, whereas 45% of hybrids were more A. sandaracinos‐like, suggesting backcrossing. Unidirectional introgression of A. chrysopterus mtDNA into A. sandaracinos via hybrid backcrosses was found, with larger female hybrids and small male A. sandaracinos mating. Potential nDNA introgression was also evident through distinct intermediate hybrid genotypes penetrating both parent species. Findings support the hypothesis that anemonefish hierarchical behaviour, habitat use and species‐specific size differences determine how hybrids form and the evolutionary consequences of hybridization.