Who resembles whom? Mimetic and coincidental look-alikes among tropical reef fishes

Comparison of mortality and feeding behavior of the false cleanerfish Aspidontus taeniatus and the lance blenny A. dussumieri regarding the effects of mimicry

Many examples of mimicry have been reported in coral reef fishes of which the most well known is the mimicry of the bluestreak cleaner wrasse, Labroides dimidiatus by the false cleanerfish, Aspidontus taeniatus. To examine the effect of protective and aggressive mimicry of A. taeniatus, mortality and feeding behavior were compared with those of the non-mimic lance blenny, Aspidontus dussumieri, by field observations on the coral reefs of Miyako Island, Okinawa, southern Japan. Survival rate of A. taeniatus was more than twice higher than that of A. dussumieri, but the detected differences were not significant, and the effect of protective mimicry could not be determined. The benthic foods common to both species (the tubeworm, Spirobranchus giganteus, and the boring clam, Tridacna crocea) were very scarce in the study sites, and the feeding behavior of the two species was clearly different: A. dussumieri pecked at the bottom substrate, whereas A. taeniatus fed on fish fins and eggs of damselfish, regardless of body size. Our findings are the first documented evidence of the effect of aggressive mimicry on biting fish fins in relation to the availability of other foods not only in small but also in large A. taeniatus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10164-022-00769-8.

Patterns of Body Shape Diversity and Evolution in Intertidal and Subtidal Lineages of Combtooth Blennies (Blenniidae)

Marine intertidal zones can be harsher and more dynamic than bordering subtidal zones, with extreme and temporally variable turbulence, water velocity, salinity, temperature, and dissolved oxygen levels. Contrasting environmental conditions and ecological opportunities in subtidal versus intertidal habitats may generate differing patterns of morphological diversity. In this study we used phylogenetic comparative methods, measurements of body length, and two-dimensional landmarks to characterize body shape and size diversity in combtooth blennies (Ovalentaria: Blenniidae) and test for differences in morphological diversity between intertidal, subtidal, and supralittoral zones. We found that subtidal combtooth blennies have significantly higher body shape disparity and occupy a region of morphospace three times larger than intertidal lineages. The intertidal morphospace was almost entirely contained within the subtidal morphospace, showing that intertidal combtooth blennies did not evolve unique body shapes. We found no significant differences in body size disparity between tidal zones, no correlations between body shape and tidal zone or body size and tidal zone, and no body shape convergence associated with tidal zone. Our findings suggest that a subset of combtooth blenny body shapes are suitable for life in both subtidal and intertidal habitats. Many species in regions of morphospace unique to subtidal combtooth blennies exhibit distinct microhabitat use, which suggests subtidal environments promoted morphological diversification via evolutionary microhabitat transitions. In contrast, limited intertidal body shape diversity may be due to strong selective pressures that constrained body shape evolution and environmental filtering that prevented colonization of intertidal zones by certain subtidal body shapes.

The false cleanerfish relies on aggressive mimicry to bite fish fins when benthic foods are scarce in their local habitat

The false cleanerfish, Aspidontus taeniatus (Blenniidae), is known for its morphological resemblance to the bluestreak cleaner wrasse Labroides dimidiatus (Labridae). It has been suggested that A. taeniatus, which acts as a mimic, can easily bite the fins of other fishes that are deceived into requesting cleaning from it or allowing it to approach them. In fact, A. taeniatus frequently utilises benthic food items, such as damselfish eggs, the Christmas tree worm Spirobranchus giganteus, and the boring clam Tridacna crocea. Although geographical variation in the reliance on aggressive mimicry (fin biting) has been reported, the factors have not been determined. We hypothesised that one of the factors is the abundance of benthic food items. To examine our hypothesis, we compared the feeding behaviour of A. taeniatus at two locations showing contrasting abundances of benthic food items in Okinawa, southern Japan. The frequency of fin biting by the small A. taeniatus in Ishigaki Island, where S. giganteus and T. crocea were very rare, was significantly higher than that in Sesoko Island, where the two food items were abundant. We conclude that the importance of aggressive mimicry in A. taeniatus varies depending on local food conditions.

Evolution: Genomic Signatures of Mimicry and Mimicry of Genomic Signatures

How new species form in the ocean, and thus what determines the diversity of fish in the sea, is not well understood. A study in Caribbean coral-reef fishes sheds light on the genomic underpinnings of diversification in the marine realm.

Evolution of Sexual Dimorphism in Tube Blennies (Teleostei: Chaenopsidae)

The study of sexual differences provides insights into selective factors operating on males and females, especially for clades exhibiting varied levels of dimorphism. Sexual differences in morphology and coloration (melanophores) were compiled for 66 of the 89 species of tube blennies (Blenniiformes, Chaenopsidae) from the systematic literature and examination of preserved specimens. Chaenopsids include essentially monomorphic species and those in which males and females differ in as many as 17 morphological and 14 coloration features. While the sexes of most species differ in coloration (at least at the time of breeding), they are morphologically similar in Acanthemblemaria, Hemiemblemaria, and Lucayablennius. While other genera exhibit an intermediate level of dimorphism, species of Coralliozetus, Cirriemblemaria, and Emblemaria are dramatically dimorphic. Character maps on a phylogenetic hypothesis indicate that this extreme level of dimorphism evolved independently in these genera. A complex history of evolution is implied by examination of jaw length with both increases and decreases in one or both sexes leading to either dimorphism or monomorphism. Several features related to shelter defense are monomorphic in species where both sexes inhabit shelters, but dimorphic where only males occupy shelters. Other dimorphic features increase the conspicuousness of male courtship and aggressive displays.

A matter of proportion? Associational effects in larval anuran communities under fish predation

In Batesian mimicry, a species lacking defences against predators benefits from mimicking the aposematic signal of a defended species, while the model may incur the costs of reduced defensive efficacy. Similar reciprocal indirect effects may emerge even when the signal is not mimicked; termed associational effects, such interactions are well known in plants sharing herbivores but have received little attention in animal studies. We investigated associational interactions in a system where unequally defended prey (chemically defended Bufo bufo and undefended Rana temporaria tadpoles), sharing general morphology but not an aposematic signal, were exposed to predation by the carp Cyprinus carpio along a gradient of relative prey abundance. In the absence of fish, the assemblage composition had no effect on the survival of Rana, while that of Bufo decreased with increasing abundance of Rana. Fish reduced the survival of tadpoles from both species. However, increased relative abundance of Bufo in the community led to enhanced survival in both Bufo and Rana. Increasing relative proportions of heterospecifics reduced metamorph mass only in Bufo, indicating greater sensitivity to interspecific competition compared to Rana; the effect was reduced in the presence of fish. Our results show that undefended non-mimetic prey enjoy reduced predation with increasing relative abundance of chemically defended prey, which in turn suffer greater mortality with an increasing proportion of the undefended species. Associational resistance/susceptibility, driven by current assemblage composition, not by selection for resemblance, can shape the dynamics of mixed communities of defended and undefended prey in the absence of mimicry.

Buccal venom gland associates with increased of diversification rate in the fang blenny fish Meiacanthus (Blenniidae; Teleostei)

At the macroevolutionary level, many mechanisms have been proposed to explain explosive species diversification. Among them morphological and/or physiological novelty is considered to have a great impact on the tempo and the mode of diversification. Meiacanthus is a genus of Blenniidae possessing a unique buccal venom gland at the base of an elongated canine tooth. This unusual trait has been hypothesized to aid escape from predation and thus potentially play an important role in their pattern of diversification. Here, we produce the first time-calibrated phylogeny of Blenniidae and we test the impact of two morphological novelties on their diversification, i.e. the presence of swim bladder and buccal venom gland, using various comparative methods. We found an increase in the tempo of lineage diversification at the root of the Meiacanthus clade, associated with the evolution of the buccal venom gland, but not the swim bladder. Neither morphological novelty was associated with the pattern of size disparification in blennies. Our results support the hypothesis that the buccal venom gland has contributed to the explosive diversification of Meiacanthus, but further analyses are needed to fully understand the factors sustaining this burst of speciation.

Temporal changes in hamlet communities (Hypoplectrus spp., Serranidae) over 17 years

Transect surveys of hamlet communities (Hypoplectrus spp., Serranidae) covering 14 000 m² across 16 reefs off La Parguera, Puerto Rico, are presented and compared with a previous survey conducted in the year 2000. The hamlet community has noticeably changed over 17 years, with a > 30% increase in relative abundance of the yellowtail hamlet Hypoplectrus chlorurus on the inner reefs at the expense of the other hamlet species. The data also suggest that the density of H. chlorurus has declined and that its distribution has shifted towards shallower depths. Considering that H. chlorurus has been previously identified as one of the few fish showing a positive association with seawater turbidity on the inner reefs of La Parguera and that sedimentation of terrestrial origin has increased over recent decades on these reefs, it is proposed that turbidity may constitute an important but so far overlooked ecological driver of hamlet communities.

Morphometric comparisons of plant-mimetic juvenile fish associated with plant debris observed in the coastal subtropical waters around Kuchierabu-jima Island, southern Japan

The general morphological shape of plant-resembling fish and plant parts were compared using a geometric morphometrics approach. Three plant-mimetic fish species, Lobotes surinamensis (Lobotidae), Platax orbicularis (Ephippidae) and Canthidermis maculata (Balistidae), were compared during their early developmental stages with accompanying plant debris (i.e., leaves of several taxa) in the coastal subtropical waters around Kuchierabu-jima Island, closely facing the Kuroshio Current. The degree of similarity shared between the plant parts and co-occurring fish species was quantified, however fish remained morphologically distinct from their plant models. Such similarities were corroborated by analysis of covariance and linear discriminant analysis, in which relative body areas of fish were strongly related to plant models. Our results strengthen the paradigm that morphological clues can lead to ecological evidence to allow predictions of behavioural and habitat choice by mimetic fish, according to the degree of similarity shared with their respective models. The resemblance to plant parts detected in the three fish species may provide fitness advantages via convergent evolutionary effects.

A complex mode of aggressive mimicry in a scale-eating cichlid fish

Aggressive mimicry is an adaptive tactic of parasitic or predatory species that closely resemble inoffensive models in order to increase fitness via predatory gains. Although similarity of distantly related species is often intuitively implicated with mimicry, the exact mechanisms and evolutionary causes remain elusive in many cases. Here, we report a complex aggressive mimicry strategy in Plecodus straeleni, a scale-eating cichlid fish from Lake Tanganyika, which imitates two other cichlid species. Employing targeted sequencing on ingested scales, we show that P. straeleni does not preferentially parasitize its models but—contrary to prevailing assumptions—targets a variety of co-occurring dissimilar looking fish species. Combined with tests for visual resemblance and visual modelling from a prey perspective, our results suggest that complex interactions among different cichlid species are involved in this mimicry system.

Comparative Allometric Growth of the Mimetic Ephippid Reef Fishes Chaetodipterus faber and Platax orbicularis

Mimesis is a relatively widespread phenomenon among reef fish, but the ontogenetic processes relevant for mimetic associations in fish are still poorly understood. In the present study, the allometric growth of two allopatric leaf-mimetic species of ephippid fishes, Chaetodipterus faber from the Atlantic and Platax orbicularis from the Indo-Pacific, was analyzed using ten morphological variables. The development of fins was considered owing to the importance of these structures for mimetic behaviors during early life stages. Despite the anatomical and behavioral similarities in both juvenile and adult stages, C. faber and P. orbicularis showed distinct patterns of growth. The overall shape of C. faber transforms from a rounded-shape in mimetic juveniles to a lengthened profile in adults, while in P. orbicularis, juveniles present an oblong profile including dorsal and anal fins, with relative fin size diminishing while the overall profile grows rounder in adults. Although the two species are closely-related, the present results suggest that growth patterns in C. faber and P. orbicularis are different, and are probably independent events in ephippids that have resulted from similar selective processes.