Variation in penis morphology and mating ability in the acorn barnacle, Semibalanus balanoides

I examined variation in penis morphology of the acorn barnacle, Semibalanus balanoides, at different aggregation densities and at different levels of wave exposure. Barnacles in sparse, un-crowded aggregations had significantly longer penises than those from densely crowded groups, suggesting a response to increase the chance of reaching distant mating partners. Barnacles exposed to oceanic waves had penises with significantly greater basal diameter, possibly to strengthen the penis and retain function in turbulent conditions. I compared the percentage of individual barnacles with fertilized broods over a range of distances to their nearest possible mate in sites exposed to or protected from waves. As neighbor distance increased, the proportion of individuals with fertilized egg masses decreased in both wave-exposed and protected sites. However, at greater mate distances in the wave exposed sites, the proportion of individuals with fertilized eggs was significantly lower than the proportion in protected sites, indicating that exposure to waves hinders mating with neighbors at increasing distances. These results suggest that the intensity of mate competition may differ for barnacles between environments with different levels of wave exposure. These differences in male ability are predicted to alter relative sex allocation to male and female function.     

Precisely proportioned: intertidal barnacles alter penis form to suit coastal wave action

For their size, barnacles possess the longest penis of any animal (up to eight times their body length). However, as one of few sessile animals to copulate, they face a trade-off between reaching more mates and controlling ever-longer penises in turbulent flow. We observed that penises of an intertidal barnacle (Balanus glandula) from wave-exposed shores were shorter than, stouter than, and more than twice as massive for their length as, those from nearby protected bays. In addition, penis shape variation was tightly correlated with maximum velocity of breaking waves, and, on all shores, larger barnacles had disproportionately stouter penises. Finally, field experiments confirmed that most of this variation was due to phenotypic plasticity: barnacles transplanted to a wave-exposed outer coast produced dramatically shorter and wider penises than counterparts moved to a protected harbour. Owing to the probable trade-off between penis length and ability to function in flow, and owing to the ever-changing wave conditions on rocky shores, intertidal barnacles appear to have acquired the capacity to change the size and shape of their penises to suit local hydrodynamic conditions. This dramatic plasticity in genital form is a valuable reminder that factors other than the usual drivers of genital diversification--female choice, sexual conflict and male-male competition--can influence genital form.     

Cuticle and muscle variation underlying phenotypic plasticity in barnacle feeding leg and penis form

Many aspects of barnacle body form are known to be developmentally plastic. Perhaps the most striking examples of such plasticity occur in their feeding legs and unusually long penises, the sizes and shapes of which can change dramatically and adaptively with changes in conspecific density and local water flow conditions. However, whether variation in overall appendage form is mirrored by structural responses in cuticle and muscle is not known. In order to determine how structural variation underlies phenotypic plasticity in barnacle appendages, we examined barnacles occurring at low and high population densities from one wave‐protected and one wave‐exposed site. We used histological sectioning and fluorescence microscopy of feeding legs and penises to compare cuticle thickness, muscle thickness, and muscle organization, and artificial penis inflation to compare penis extensibility. We observed striking differences in cuticle thickness, muscle thickness, and muscle organization between sites that differed in water velocity, but we found no clear differences associated with variation in conspecific density. Penis extensibility also did not differ consistently between sites. These results are consistent with an adaptive explanation for much of the remarkable and complex variation in barnacle feeding leg and penis morphology among sites that differ in water velocity.     

Dramatic phenotypic plasticity in barnacle legs (Balanus glandula Darwin): magnitude,age dependence,and speed of response

Abstract.— The precise dependence of barnacle leg form on flow suggests the wave-swept environment imposes strong selection on suspension feeding limbs. I conducted three experiments to determine the mechanism, age dependence, and response time of cirrus variation in the acorn barnacle Balanus glandula . (1) To test whether cirrus variation arises via genetic or environmental mechanisms, I transplanted juvenile barnacles from one wave-exposed and one protected population into high and low flow conditions. Both populations exhibited similar abilities to modify cirri in response to experimental velocities: transplanted barnacles grew legs up to 84% longer in low flow. A small (up to 24%), but significant difference between source populations suggested slight genetic divergence in leg form. (2) Because flow is heterogeneous over space and time, I tested whether cirrus plasticity was limited to juveniles by transplanting both juveniles and adults from exposed and protected shores into quiet water. Remarkably, both juveniles and adults from the wave-exposed population produced legs over 100% longer than the original population, whereas protected barnacles remained unchanged. (3) A third transplant of adults into quiet water demonstrated that wave-exposed B. glandula modified cirrus form very quickly-within 18 days, or one to two molts. Results from these experiments suggest that variation in cirrus form is largely environmentally induced, but genetic differences may account for some variation observed among field populations; spatial and temporal flow heterogeneity appear to have selected for extreme flexibility of feeding form throughout a barnacle's life; and flow heterogeneity in the wave-swept environment appears to have selected for rapid ecophenotypic responses in the form of feeding structures.     

The unexpected mating system of the androdioecious barnacle Chelonibia testudinaria (Linnaeus 1758)

Androdioecy was first described by Darwin in his seminal work on barnacle diversity; he identified males and hermaphrodites in the same reproductive population. Today, we realize that many androdioecious plants and animals share astonishing similarities, particularly with regard to their evolutionary history and mating system. Notably, these species were ancestrally dioecious, and their mating system has the following characteristics: hermaphrodites self‐fertilize frequently, males are more successful in large mating groups, and males have a mating advantage. A male mating advantage makes androdioecy more likely to persist over evolutionary times. Androdioecious barnacles, however, appear to persist as an outlier with a different evolutionary trajectory: they originate from hermaphroditic species. Although sexual systems of androdioecious barnacles are known, no information on the mating system of androdioecious barnacles is available. This study assessed the mating system of the androdioecious barnacle Chelonibia testudinaria. In contrast to other androdioecious species, C. testudinaria does not self‐fertilize, males do not have a mating advantage over hermaphrodites, and the average mating group is quite small, averaging only three individuals. Mating success is increased by proximity to the mate and penis length. Taken together, the mating system of C. testudinaria is unusual in comparison with other androdioecious plants and animals, and the lack of a male mating advantage suggests that the mating system alone does not provide an explanation for the maintenance of androdioecy in this species. Instead, we propose that sex‐specific life history equalizes male and hermaphroditic overall fitness.     

When dwarf males and hermaphrodites copulate: first record of mating behaviour in a dwarf male using the androdioecious barnacle <Emphasis Type="Italic">Scalpellum scalpellum</Emphasis> (Crustacea: Cirripedia: Thoracica)

Mating behaviour between a dwarf male and its hermaphrodite partner was observed for the first time in cirripedes using the androdioecious barnacle Scalpellum scalpellum. Mating between hermaphrodites was also observed. The dwarf males are located on the rim of the mantle cavity of the hermaphrodite partner. When mating, the male extends the penis, which is four times longer than its body. The penis first assumes a straight stance where it is waved around in a searching mode. Upon touching the cirri of the hermaphrodite, the penis and the cirri engage in prolonged contact during which hermaphrodite feeding is suspended. Thereafter the penis assumes a U-bend to reach into the brood chamber, where after the mantle valves are closed tightly around the penis. The nearly transparent penis is a tube of very thin cuticle, equipped with pairs of side branches but not containing any visible tissue. The penis enables the minute male, situated outside the brood chamber, to securely deposit sperm into its partner. Adjacently situated hermaphrodites interact socially in between feeding sessions by reorienting themselves on the peduncle to touch each other with their cirri. This can be followed by precopulatory behaviour, where one or both individuals extend the penis to touch their partner, leading again to actual copulation where the penis of one individual is inserted into the other. We discuss the results in the context of the diverse reproductive strategies found in cirripede barnacles.     

ADAPTIVE PLASTICITY OF THE PENIS IN A SIMULTANEOUS HERMAPHRODITE

Acorn barnacles are important model organisms for the study of sex allocation. They are sessile, nonselfing hermaphrodites that copulate with penises that have been suggested to be phenotypically plastic. On wave-exposed shores, Semibalanus balanoides develop penises with relatively greater diameter whereas in wave-protected sites they are thinner. A reciprocal transplant experiment between wave-exposed and protected sites tested whether these exposure-specific morphologies have adaptive value. Mating success was compared over a range of distances to compare the ability of barnacles to reach mates. Barnacles that grew in the wave-protected site and mated in the wave-protected site fertilized more broods at increasing distances than those transplanted to the wave-exposed site. For barnacles that developed in the wave-exposed site, there was no difference in the ability to fertilize neighbors between sites of differing exposure. This study demonstrates the adaptive value of plasticity in penis morphology. The results suggest a trade-off between development of a penis adapted to wave exposure and the ability to fertilize distant mates. Barnacles in different physical environments are limited by different factors, which may limit numbers of potential mates, constrain optimal sex allocation strategies and alter reproductive behavior.     

Something Darwin didn't know about barnacles: spermcast mating in a common stalked species

Most free-living barnacles are hermaphroditic, and eggs are presumed to be fertilized either by pseudo-copulation or self-fertilization. Although the common northeast Pacific intertidal gooseneck barnacle, Pollicipes polymerus, is believed only to cross-fertilize, some isolated individuals well outside penis range nonetheless bear fertilized eggs. They must therefore either self-fertilize or—contrary to all prior expectations about barnacle mating—obtain sperm from the water. To test these alternative hypotheses, we collected isolated individuals bearing egg masses, as well as isolated pairs where at least one parent carried egg masses. Using 16 single nucleotide polymorphism markers, we confirmed that a high percentage of eggs were fertilized with sperm captured from the water. Sperm capture occurred in 100 per cent of isolated individuals and, remarkably, even in 24 per cent of individuals that had an adjacent partner. Replicate subsamples of individual egg masses confirmed that eggs fertilized by captured sperm occurred throughout the egg mass. Sperm capture may therefore be a common supplement to pseudo-copulation in this species. These observations (i) overturn over a century of beliefs about what barnacles can (or cannot) do in terms of sperm transfer, (ii) raise doubts about prior claims of self-fertilization in barnacles, (iii) raise interesting questions about the capacity for sperm capture in other species (particularly those with short penises), and (iv) show, we believe for the first time, that spermcast mating can occur in an aquatic arthropod.     

Variation in barnacle recruitment over small scales: larval predation by adults and maintenance of community pattern

Over small spatial scales, variation in the density of settlers of benthic sessile species is the result of interactions among larval behavior, local hydrodynamic conditions, and the physical, chemical and biological characteristics of the benthic habitat. It has been shown repeatedly that adult benthic filter-feeders can consume larvae of their own and other species, but their effects on the distribution and abundance of recruits have rarely been demonstrated under natural conditions in the field, particularly on hard substrata. Here we experimentally quantified the effect of the large intertidal barnacle, Semibalanus cariosus (Pallas), on the density of recruits of three common barnacle species. The experiments were conducted at the peak of the barnacle recruitment season over three successive years, on the west coast of San Juan Island, Washington. A persistent and well documented community pattern in the mid intertidal zone of the study site is a sparse bed of adult S. cariosus with bare rock spaces essentially devoid of small barnacles among the large individuals. Field experiments consisted of small areas from which either all adult S. cariosus were killed leaving the shells attached to the rock, or live adult barnacles were left intact. Our results showed that over small spatial scales of a few to tens of centimeters, the large barnacle S. cariosus can interfere and significantly reduce net settlement and recruitment of conspecific as well as other barnacle species. Between 65 and 100% reduction in settlement could be attributed to larval predation by adults, as implied by barnacle settlement patterns on different treatments and by the presence of nauplius larvae in cirri and stomach contents of S. cariosus. The negative effect on barnacle settlement was consistent between years of relatively low barnacle recruitment, which appears to be the most common situation at the study site, but it disappeared on a year of unusually high recruitment, when settling larvae seem to have swamped the filtration ability of adult S. cariosus. The different barnacle species displayed contrasting settlement patterns on bare rock and on the lateral shells of the large barnacles, which appear to be a result of differences in larval behavior. Comparisons against the relative availability of these substrata in the experimental plots suggested that larvae of different species sample the benthic microhabitat in very different ways.     

The vertical distribution of Chthamalus montagui and Chthamalus stellatus (Crustacea,Cirripedia) in two areas of the NW Mediterranean Sea

The Mediterranean Sea is characterised by a small tidal range (0.3–1 m). Despite this, intertidal communities are well established and their upper limits often extend above mean high water level. Organisms living in the intertidal region and in the supralittoral zone rely on both tides and wave action to perform their biological functions. Lack of food, desiccation and predation are common stresses in such a harsh environment. The present study deals with the vertical distribution of two species of intertidal barnacles, Chthamalus montagui Southward and Chthamalus stellatus (Poli), which are the main constituents of the barnacle belt along Mediterranean rocky shores. Previous work, carried out in the Atlantic, showed that where the distribution ranges of the two Chthamalus species overlap, C. montagui is more common in the upper barnacle zone while C. stellatus is dominant lower down. The main aims of our study are: (1) to establish if there is a relationship between position and extension of the barnacle belt on the shore and tidal range and/or wave exposure, (2) to test the hypothesis that in the study areas C. montagui is more abundant than C. stellatus high on the shore, and that the pattern is reversed lower down. Barnacle populations were monitored in summer 1998 in the Gulf of Genoa (Ligurian Sea) and in the Gulf of Trieste (North-Adriatic Sea). The two areas differ in tidal range and hydrodynamism, the former presenting quite strong wave action and a tidal range of 30 cm, the latter having limited wave action and 1 m tidal range. Three shores were randomly selected in each gulf and two transects on each shore. Counts of barnacles in 10 ^* 10 cm quadrats were done at different shore heights along each transect. The data was subjected to analysis of variance. Results showed that a more pronounced hydrodynamic regime corresponded to a shift of the barnacle belt towards the higher shore (Gulf of Genoa), while in more sheltered areas (Gulf of Trieste), the barnacle distribution was confined to the intertidal region. The relative spatial distribution of C. montagui and C. stellatus within the barnacle belt varied locally, even between transects on the same shore, and this obscured the distribution pattern along the vertical gradient. Nevertheless, it was still possible to conclude that at mid and high shore in Genoa, C. stellatus was more abundant than C. montagui, while in Trieste the pattern was reversed.     

Gene rearrangement and sequence analysis of mitogenomes suggest polyphyly of Archaeobalanid and Balanid barnacles (Cirripedia: Balanomorpha)

The acorn barnacles (Cirripedia, Thoracica, Balanomorpha) are a diverse group of crustaceans found in virtually all marine and estuarine habitats. Barnacles are important model species in various biological researches, including evolution, intertidal ecology, larval biology and antifouling. However, there remains a lack of a thorough understanding of the phylogeny for this group of animals, particularly at higher taxonomic levels. In this study, we attempt to determine the phylogenetic relationships among balanomorphan families based on analysis of complete mitochondrial genome from various barnacle families and investigate the evolution of mitogenome in barnacles. Whole mitogenomes of six barnacles were newly sequenced, including Acasta sulcata (Archaeobalanidae), Armatobalanus allium (Archaeobalanidae), Chelonibia testudinaria (Chelonibiidae), Octomeris sp. (Chthamalidae), Savignium biporata (Pyrgomatidae) and Tetraclitella divisa (Tetraclitidae), which exhibit five different gene arrangements. Phylogenetic analysis on 15 complete mitochondrial genome sequences from major barnacle families supported Chthamalidae, Pyrgomatidae and Tetraclitidae formed monophyletic units, but suggested polyphyly of both Archaeobalanidae and Balanidae. Chthamalidae was the earliest diverged lineage in Balanomorpha. Chelonibiidae + Tetraclitidae formed the sister taxon to the monophyletic superfamily Balanoidea (Archaeobalanidae + Balanidae + Pyrgomatidae). The members of Archaeobalanidae and Balanidae intermingled in the inferred topology with the monophyletic Pyrgomatidae deeply nested within. Two Megabalanus species from the family Balanidae and A. sulcata from the family Archaeobalanidae share the same six‐gene‐cluster inversion as compared to the other ten balanomorphan barnacles, providing further evidence for the non‐monophyly for the two families. We showed here that the informativeness of the complete mitogenome sequence and rare genomic events in resolving various questions concerning Balanomorpha relationships. The non‐monophyletic status of Archaeobalanidae and Balanidae falsified many previous hypotheses concerning the complex evolution of Balanomorpha and call for further investigations and careful revision on the taxonomy of the group. Future study focusing on the enigmatic and tentatively basal lineages, for example, Chionelasmatoidea Pachylasmatoidea and Catophragmidae, would be most helpful in fully resolving the phylogeny and mitogenome evolutionary history of acorn barnacles.     

Tetraclita ehsani sp. n. (Cirripedia, Tetraclitidae), a common intertidal barnacle from the Gulf of Oman, Iran

A new species of intertidal acorn barnacle Tetraclita ehsanisp. n. was identified from the Iranian coast in the Gulf of Oman. Tetraclita ehsanisp. n. inhabits low exposed rocky shores and also attaches to shells of molluscs and the barnacle Megabalanus species. Parietes of Tetraclita ehsani ranged from white to pink which is different from Tetraclita serrata (in South African waters), which has green parietes. Morphology of the tergum and cirrus III of Tetraclita ehsanisp. n. is distinctive from other described West Indian Ocean species which have pink or white parietes (Tetraclita rufotincta, Tetraclita achituvi and Tetraclita reni). The tergum of Tetraclita ehsani is very narrow and the basal margin is slightly concave or straight, in contrast to Tetraclita rufotincta and Tetraclita reni, in which the tergum are board and with a very concave basal margin. Cirrus I anterior ramus of both Tetraclita ehsani and Tetraclita reni is antenniform and thus differing from the cirrus I of Tetraclita rufotincta (see Chan et al. 2009). Cirrus III of Tetraclita ehsanisp. n. is non-antenniform and lacks multicuspidate type setae, which is different from Tetraclita reni by having an antenniform cirrus III and with multicuspidate setae.     

Intertidal and Subtidal Fouling Assemblages in a Patagonian Harbour (Argentina, Southwest Atlantic)

The composition of the early stages of intertidal and subtidal fouling assemblages in Comodoro Rivadavia harbour (Argentina, 45°52′ S, 67°28′ W) and the influence of shore level and season on their structure were analysed. At the beginning of each season, stones were glued to the substratum with epoxy putty and distributed along 4 vertical transects at intervals of 20 m, at 3 levels: upper intertidal, middle intertidal, and subtidal. Substrata remained in the field for 84–100 days. A total of 48 samples (4 seasons × 3 levels × 4 replicates) were analysed. Species richness increased with depth, with 6 taxa in the upper intertidal, 23 in the middle intertidal and 31 in the subtidal. Seasonal differences in richness were less distinct. Green, red and brown algae were the dominant groups. Invertebrates were mainly represented by filter-feeding, sessile organisms, such as cheilostome bryozoans, spirorbid polychaetes and acorn barnacles. The barnacle Balanus glandula and the bryozoan Cryptosula pallasiana were the only non-indigenous species found in this study. Highly significant differences in structure among shore levels and seasons were evidenced by a two-way ANOSIM test. The upper intertidal is characterized by the filamentous green algae Urospora penicilliformis and Ulothrix flacca. The barnacle Balanus glandula is the most abundant species in the middle intertidal. The subtidal is defined mainly by the presence of the spirorbid polychaetes Paralaeospira levinseni and Romanchella perrieri, and the keyhole limpet Fissurella radiosa. Ordination of samples by season was less clear than by shore level.     

Comparative analysis of barnacle tropomyosin: divergence from decapod tropomyosins and role as a potential allergen

Tropomyosin, a myofibrillar protein of 35-38 kDa, represents a major and cross-reactive allergen in decapod crustaceans. This study was initiated to clarify whether decapod-allergic patients also recognize tropomyosins of barnacles, crustaceans phylogenetically remote from decapods, which are locally consumed as a delicacy. On SDS-PAGE, a 37 kDa protein was observed in all the heated extracts prepared from two species of decapods (American lobster Homarus americanus and black tiger prawn Penaeus monodon) and two species of barnacles (acorn barnacle Balanus rostratus and goose barnacle Capitulum mitella). In immunoblotting, the 37 kDa protein was found to react with monoclonal antibodies against American lobster tropomyosin and hence identified as tropomyosin. The patient sera reacted to tropomyosins from both decapods and barnacles and the reactivity was abolished by preincubation with American lobster tropomyosin, demonstrating that barnacle tropomyosins are allergens cross-reactive with decapod tropomyosins. However, the amino acid sequence of acorn barnacle tropomyosin, deduced by cDNA cloning experiments, shares higher sequence identity with abalone tropomyosins than with decapod tropomyosins. In accordance with this, the phylogenetic tree made for tropomyosins from various animals showed that the acorn barnacle tropomyosin is evolutionally classified not into the decapod tropomyosin family but into the molluscan tropomyosin family.     

How recruitment, intraspecific interactions, and predation control species borders in a tidal estuary

We examined the relative contribution of recruitment, intraspecific species interactions, and predation in controlling the upper intertidal border of the northern acorn barnacle, Semibalanusbalanoides, in a tidal estuary in Maine. We hypothesized that the contracted border at sites that experienced low tidal currents was due to flow-mediated recruitment that resulted in reduced survival due to the absence of neighbor buffering of thermal stress (i.e., positive intraspecific interactions). We tested this hypothesis by manipulating the density of recently settled barnacles and their thermal environment in a field experiment. Counter to our original hypothesis, barnacles with neighbors suffered severe mortality at low-flow sites. When density-dependent predation by the green crab (Carcinusmaenus) was experimentally eliminated, however, we did detect evidence for positive interactions at the low-flow sites but not at the high-flow sites. In spite of the close proximity of the sites, maximum daily rock temperatures at the low-flow sites were slightly, but consistently, greater than those at high-flow sites. Our findings suggest that the upper intertidal border of S. balanoides in the Damariscotta River is limited at low-flow sites by a combination of reduced recruitment, elevated mortality from thermal stress and enhanced predation by green crabs. More generally, our findings highlight how physical stress and predation interact to alter the nature of density-dependent species interactions in natural assemblages. Received: 6 August 1998 / Accepted: 11 October 1998     

Regional variation in the spatial scale of selection at MPI* and GPI* in the acorn barnacle Semibalanus balanoides (Crustacea)

Elucidating the ecological processes by which adaptive genetic polymorphism is maintained in heterogeneous environments requires knowledge on the spatial scale at which alternate habitats affect genotype-specific fitness. The general objective of this study was to document patterns of temporal and spatial variation of genetic polymorphism in the acorn barnacle (Semibalanus balanoides) at MPI* and GPI* allozyme loci. A total of 7261 barnacles were sampled in the intertidal at various locations north and south of the Miramichi estuary, New Brunswick, Canada. The results of this study supported the hypothesis that both MPI* and GPI* are under the effect of strong directional selection south of the Miramichi, whereas neutrality cannot be ruled out at sampling sites located north of the estuary. Comparisons between this study and previous ones also question the generality of current hypotheses regarding ecological processes that are responsible for maintaining polymorphism at MPI* and GPI* in the acorn barnacle.     

Growth and development of the barnacle Amphibalanus amphitrite: time and spatially resolved structure and chemistry of the base plate

The radial growth and advancement of the adhesive interface to the substratum of many species of acorn barnacles occurs underwater and beneath an opaque, calcified shell. Here, the time-dependent growth processes involving various autofluorescent materials within the interface of live barnacles are imaged for the first time using 3D time-lapse confocal microscopy. Key features of the interface development in the striped barnacle, Amphibalanus (= Balanus) amphitrite were resolved in situ and include advancement of the barnacle/substratum interface, epicuticle membrane development, protein secretion, and calcification. Microscopic and spectroscopic techniques provide ex situ material identification of regions imaged by confocal microscopy. In situ and ex situ analysis of the interface support the hypothesis that barnacle interface development is a complex process coupling sequential, timed secretory events and morphological changes. This results in a multi-layered interface that concomitantly fulfills the roles of strongly adhering to a substratum while permitting continuous molting and radial growth at the periphery.     

Experimental tests of sex allocation theory with two species of simultaneously hermaphroditic acorn barnacles

Sex allocation theory for simultaneous hermaphrodites predicts increases in relative allocation to male-specific function as competition for fertilizations increases. Theoretical models developed specifically for competing acorn barnacles predict that the proportional allocation to male function increases toward an asymptote of 50% as the number of competitors for fertilizations increases. Experimental manipulations were used to investigate how mate competition affected both relative and absolute allocation to the sex functions for two species of acorn barnacle: Semibalanus balanoides and Balanus glandula. The ratio of male to female allocation did not increase with the number of competitors for either species. However, both species showed increased allocation to male function (estimated as total mass of sex-specific tissues) with increased crowding. Allocation to female function seemed to be limited by other factors and did not vary with mating group size as predicted. Allocation to male and female function were both positively related to body size, but a trade-off between male and female function, a key assumption of prior models, was not observed.     

Distribution and abundance of the acmaeid limpet,Patelloida latistrigata,and its interaction with barnacles

Summary At Cape Banks, New South Wales, adults of the small intertidal limpet, Patelloida latistrigata occur exclusively in the barnacle zone, and are primarily associated with the barnacle, Tesseropora rosea. Limpet density increases with barnacle density. Juvenile limpets can be found throughout the barnacle zone, and on patches of bare rock that may be temporarily available at lower levels on the shore. The failure of juveniles to survive and grow in places other than among Tesseropora is due to a combination of factors. These include desication at high levels on the shore, smothering by rapidly growing algae low on the shore, and the grazing activities of the larger limpet, Cellana tramoserica. These latter two factors also reduce the survival of experimentally transplanted adult Patelloida: algae by covering the substratum and smothering the limpets, and Cellana by outcompeting them for food. The density of Cellana is greater on patches of bare rock than among barnacles, and these large limpets may be unable to move and feed effectively over the irregular surface created by Tesseropora. Patelloida, however, is small enough to feed over and among these barnacles, and hence has a refuge from competition with Cellana. Barnacles may also provide shelter from the effects of desiccation and strong wave action, and thus increase the survival of juvenile Patelloida. By being associated with barnacles, however, Patelloida becomes vulnerable to intermittent predation by the whelk, Morula marginalba. This effect may be serious enough to eliminate small local populations of limpets, either by direct predation or by removing the refuge-providing barnacles. The association with barnacles may also limit the maximum size to which Patelloida can grow. Patelloida is not always found with Tesseropora, and adults in different localities can be found in association with other sessile organisms. It may be argued that small species of limpets require a spatial refuge from physical and/or biological pressures. To examine this hypothesis, the relationship between Patelloida and Tesseropora is compared to other published accounts of limpets with specialised modes of life.     

Right-handed penises of the earwig Labidura riparia (Insecta, Dermaptera, Labiduridae): evolutionary relationships between structural and behavioral asymmetries

The number of penises vary in the insect suborder Forficulina (order Dermaptera; earwigs). Males of the families Diplatyidae, Pigidicranidae, Anisolabididae, Apachyidae, and Labiduridae have two penises (right and left), while those of the Spongipohridae, Chelisochidae, and Forficulidae have a single penis. The proposed phylogenetic relationships among these families suggest that the single‐penis families evolved from an ancestor possessing two penises. To date, examinations of double‐penis earwig species have found that only a single penis is used per single copulation. These diversities in structural and behavioral aspects of genitalia raises the following intriguing questions: How are the two penises used? Why did a penis degenerate in several earwig families, and which one was lost? To address these questions, structural and behavioral asymmetries were examined in detail for a representative species Labidura riparia (Labiduridae). Although there was no detectable morphological differentiation between the right and left penises, male L. riparia predominantly used the right one for insemination. This significant “right‐handedness” developed without any experience of mating and was also manifested in the resting postures of the two penises when not engaged in copulation. However, surgical ablation of the right penis did not influence the insemination capacity of males. In wild‐caught males, only about 10% were left‐handed; within this group, abnormalities were frequently observed in the right penis. These lines of evidence indicate that the left penis is merely a spare intromittent organ, which most L. riparia males are likely never to use. Additional observations of five species of single‐penis families revealed that the left penis degenerated in the common ancestor of this group. Considering the proposed sister relationship between the Labiduridae and the single‐penis families, it is possible that such behavioral asymmetries in penis' use, as observed in L. riparia, are parental to the evolutionary degeneration of the infrequently used left penis. J. Morphol., 2006. © 2006 Wiley‐Liss, Inc.