Adaptive evolution of crustin antimicrobial peptides in decapods

Antimicrobial peptides (AMPs) are present in a wide range of taxonomic groups and played a crucial role in host adaptation to a diverse array of ever-changing pathogens. Crustin, a cysteine-rich cationic AMP, is known to exhibit antimicrobial activity against Gram-positive and Gram-negative bacteria in decapods. Given their important role in host-immune defense, a large proportion of amino acid substitutions in crustin AMPs are expected to be fixed by natural selection. Utilizing the complete coding nucleotide sequence data of crustin, the present study revealed the pervasive role of positive Darwinian selection in the evolution and divergence of crustin AMPs in decapods. Approximately, 20–35?% of codons in two phylogenetically distinct groups of closely related crustins in Penaeid shrimps are shown to have evolved under positive selection. Interestingly, several of these positively selected sites are located at the carboxyl-terminal region, the region that directly interacts with the invading pathogens. Pathogen-mediated selection pressure could be the likely cause for such an accelerated rate of amino acid substitutions and could have contributed to the structural and functional diversification of crustin AMPs in several taxa.     

Functional morphology of the cuticular terraces in burrowing terrestrial brachyuran decapods

Observations on Gecarcinus lateralis and Ocypode quadrata from Bermuda show that their cuticular terraces are not functional as burrowing sculptures, as previously assumed. Instead, they increase the friction against the walls of the burrow when the animal wedges itself to avoid being extracted by predators. No significant increase in the number of terraces takes place during growth in the size interval available for this study. This is different from the situation described as usual in burrowing decapods, and is rather similar to that of crevice-dwelling crabs. The distribution of terraces and their ontogenetic pattern, therefore, are not reliable indicators of the life habits.     

Development and functional morphology of the foreguts of larvae and postlarvae of three crustacean decapods

The development of the foregut structure and the digestive function of the decapods Litopenaeus vannamei, Sesarma rectum and Callichirus major larvae and post larvae were examined. The protozoeal foregut of L. vannamei is simple, lacking a cardiopyloric valve and bearing a rudimentary filter press. In mysis, the filter press is more developed. In the juvenile stage, grooves and a small lateral tooth arise. In S. rectum, the foregut has a functional cardiopyloric valve and a filter press. The megalopal and juvenile stages of this species have a gastric mill similar to those in adult crabs. In C. major, the foregut of the zoeae is specialized, with the appearance of some rigid structures, but no gastric mill was found. Calcified structures are observed in the megalopae and they become more developed in the juvenile stage. The results support suppositions, previously reported in other studies, that feeding behavior of each larval and postlarval stage is directly related to the morphological characteristics of the foreguts.     

The comparative evolution of lizard claw and toe morphology and clinging performance

In this study, I utilize the expected functional relationships between claw and toe morphology and clinging performance as a basis for examining evolutionary trends across 85 lizard taxa from 13 families. After controlling for body size and phylogeny, multivariate comparisons indicate that several aspects of claw and toe morphology are correlated with clinging performance. Specifically, evolutionary increases in claw curvature, toe width and adhesive lamella number are correlated with increases in clinging performance on smooth substrates. Furthermore, evolutionary increases in claw height and decreases in toe length are correlated with increases in clinging performance on rough substrates. Sensitivity analyses revealed that changes in both branch lengths and procedural order of correction for body size and phylogeny do not generally have an effect on phylogenetic comparisons. These results demonstrate that the evolution of claw and toe morphology is correlated with the evolution of clinging performance across a wide range lizard taxa.     

A comparative analysis of the morphology and evolution of permanent sperm depletion in spiders

Once thought to be energetically cheap and easy to produce, empirical work has shown that sperm is a costly and limited resource for males. In some spider species, there is behavioral evidence that sperm are permanently depleted after a single mating. This extreme degree of mating investment appears to co-occur with other reproductive strategies common to spiders, e.g. genital mutilation and sexual cannibalism. Here we corroborate that sperm depletion in the golden orb-web spider Nephila clavipes is permanent by uncovering its mechanistic basis using light and electron microscopy. In addition, we use a phylogeny-based statistical analysis to test the evolutionary relationships between permanent sperm depletion (PSD) and other reproductive strategies in spiders. Male testes do not produce sperm during adulthood, which is unusual in spiders. Instead, spermatogenesis is nearly synchronous and ends before the maturation molt. Testis size decreases as males approach their maturation molt and reaches its lowest point after sperm is transferred into the male copulatory organs (pedipalps). As a consequence, the amount of sperm available to males for mating is limited to the sperm contained in the pedipalps, and once it is used, males lose their ability to fertilize eggs. Our data suggest that PSD has evolved independently at least three times within web-building spiders and is significantly correlated with the evolution of other mating strategies that limit males to monogamy, including genital mutilation and sexual cannibalism. We conclude that PSD may be an energy-saving adaptation in species where males are limited to monogamy. This could be particularly important in web-building spiders where extreme sexual size dimorphism results in large, sedentary females and small, searching males who rarely feed as adults and are vulnerable to starvation. Future work will explore possible energetic benefits and the evolutionary lability of PSD relative to other mate-limiting reproductive behaviors.     

Aspects of the structure and development of monotreme spermatozoa and their relevance to the evolution of mammalian sperm morphology

Summary The elongated spermatid nuclei of monotremes exhibit a circumferentially arranged spiral pattern of chromatin condensation, and ultimately form helical filiform sperm heads up to 50 m long and either circular or slightly oval in transverse section. The acrosome is formed by the collapse of the proacrosomal vacuole onto the rostral surface of the elongating nucleus. However, genesis of acrosomal material occurs in the absence of a prominent proacrosomal granule. The flagellum becomes inserted into the distal extremity of the nucleus, the most proximal mitochondria of the midpiece directly abutting the nuclear membrane, so that a prominent neck region is absent. The axoneme is simple and, in the midpiece, small dense peripheral fibres are closely applied to the outer surface of each of the nine microtubule doublets. The cortical fibrous sheath of the principal piece is an anastomosing spiral that lacks lateral columnar elements.The spermatozoal cytoplasmic droplet undergoes migration and is lost during epididymal passage.Monotreme spermatozoa exhibit a montage of features, some of these being also found in marsupials and some in sauropsidan vertebrates, as well as a number of their own distinctive features. It is concluded that monotreme spermatozoa also have a close affinity with the unspecialised spermatozoa of some eutherian mammals.We wish to thank Dr. Mervyn E. Griffiths for providing the Zaglossus material. Permits to collect these native mammals were provided by the National Parks and Wildlife Services, and State Fisheries Services of New South Wales and Queensland. Portion of this work was supported by grants from the Australian Research Grants Committee. The provision of skilled technical assistance and access to electron microscope facilities were kindly provided by Dr. C.D. Shorey, formerly Acting Director of the University of Sydney Electron Microscope Unit, and by Mr. John Hardy, Senior Lecturer-in-Charge of the University of Queensland Electron Microscope Centre. Members of the technical staff of the Departments of Anatomy and Veterinary Anatomy are also acknowledged for their assistance     

Rapid divergent evolution of sexual morphology: comparative tests of antagonistic coevolution and traditional female choice

Male structures specialized to contact females during sexual interactions often diverge relatively rapidly over evolutionary time. Previous explanations for this pattern invoked sexual selection by female choice, but new ideas emphasize possible sexually antagonistic coevolution resulting from male-female conflict over control of fertilization. The two types of selection have often not been carefully distinguished. They do not theoretically exclude one another, but they have not necessarily had equally important roles in producing rapid evolutionary divergence. To date, most recent empirical studies of antagonistic coevolution have emphasized only a few taxa. This study uses the abundant but little-used data in the taxonomic literature on morphology to evaluate the roles of antagonistic coevolution and traditional female choice over a wide taxonomic spectrum (61 families of arthropods, mostly insects and spiders). Groups with species-specific male structures that contact females were checked for coevolution of species-specific female structures that are contacted by the male and that have mechanical properties that could potentially defend her against the male. Facultatively deployable, species-specific female defensive structures, a design that would seem likely to evolve frequently under the sexually antagonistic coevolution hypothesis, were completely absent (0% of 106 structures in 84 taxonomic groups). Although likely cases of sexually antagonistic coevolution exist, using conservative criteria, 79.2% of the 106 structures lacked even potentially defensive female coevolution. A common pattern (53.8% of 106) was a nearly complete absence of female change in areas contacted by species-specific male structures. Post-hoc arguments invoking possible coevolution of defensive female behavior instead of morphology, or of female sensitivities and responses to male sensory traps, could enable the sexually antagonistic coevolution hypothesis to explain these data. No case of such coevolution of female behavior or sensitivities has been demonstrated, and there are additional reasons to doubt that they are general explanations for the data presented here. Detailed studies of female resistance behavior could help illuminate several issues. The possibility of a greater role for antagonistic coevolution in reproductive physiology than in morphology and the possibility that female choice and sexually antagonistic coevolution have both been important in some lineages are discussed.     

The comparative morphology and evolution of the eyes of caecilians (Amphibia,Gymnophiona)

Summary Caecilians (Amphibia, Gymnophiona) have been reported to have vestigial eyes, to lack some or all of the extrinsic eye muscles and their nerves, and to utilize eye muscles and glands, or derivatives of them, to effect movement of the tentacle, a chemosensory structure unique among vertebrates. Morphological evidence indicates that the eye is a functional photoreceptor in virtually all species examined, with an intact retina and optic nerve. The pattern of retention of extrinsic muscles varies. The ontogeny of the eye of Dermophis mexicanus is typical of that of most vertebrates, though components of accommodation never develop. Several taxa are reported in the literature to lack various eye structures; the present study reveals them to be variously present. Evolutionary trends in caecilian eye morphology include the following: (1) the eye is overlain by thicker, often glandular skin, to overlain by bone as well as skin; (2) extrinsic muscles become attenuate, and some to all may be lost; (3) the retina has the typical vertebrate layered organization, to having a reduced cell number, to becoming net-like rather than stratal; (4) the optic nerve is present, becoming attenuate, perhaps represented only by glial cells; (5) the lens is round (aquatic forms, larval and adult) to spheroid; lens crystalline to cellular (retention of the embryonic condition) to amorphous to absent; (6) the vitreous body is reduced or lost; (7) the cornea adheres to the overlying dermis or periosteum; the lens is free to adherent to cornea to adherent to both cornea and retina. Scolecomorphids have the eye pulled out of the socket and embedded in the tentacle under the skin of the upper jaw. This pattern of trends in eye reduction is similar to that observed in other vertebrate lineages that are fossorial or troglobitic.     

On the morphology of spermatozoa of tuco-tucos, Ctenomys (Rodentia: Ctenomyidae): New data and its implications for the evolution of the genus

Sperm morphology was studied in 10 species of the caviomorph rodent Ctenomys. Ctenomys argentinus, C. conoueri, C. dorbigny and C.perrensis had symmetric spermatozoa with paddle-like heads. Ctenomys australis, C. mendocinus, C. porteousi, C. rionegrensis and Ctenomys sp., on the other hand, had spermatozoa with paddle-like heads but with the tail inserted at one side of the central axis and a nuclear caudal extension originating from the base of the head at the opposite side of the insertion of the tail and running parallel to the flagellum; these spermatozoa are referred to as simple-asymmetric. In C. yolandae, a complex-asymmetric morphological type not previously described for the genus was found. This type is characterized by the presence of two nuclear caudal extensions. Symmetric spermatozoa (total length = 52 pm) were shorter than asymmetric (both simple and complex) ones (total length = 87 pm). In spite of these differences, the relative size of heads, midpieces and tails were maintained in the three groups, representing 12%, I I YO and 88% of the average total length, respectively. Within each group of species bearing the same sperm type, a low interspecific variability both in morphological patterns and dimensions of sperm cells was observed. This low interspecific variability associated with the north to south geographical distribution of species having, respectively, symmetric and asymmetric spermatozoa, suggests that these characters appeared at an early stage in evolution of the group, and probably played an important role in the first steps of speciation by promoting reproductive isolation.     

Molecules and morphology: comparative developmental genetics of the Brassicaceae

For approximately 20 years Arabidopsis has been a model system to investigate developmental and physiological questions in plant biology, leading to the identification of genes and genetic systems involved in many processes. Extending ideas arising from knowledge of developmental genetic systems in Arabidopsis to other species of the Brassicaceae will require the application of genomics technologies developed in Arabidopsis and the establishment of additional genetic systems and resources in other species. Morphological variation in all plant organs, as well as in growth habit, mating systems, and physiology are represented in the breadth of Brassicaceae species offering ample opportunity to investigate the molecular basis of morphological evolution in this family. In addition, the frequent recent hybridization events in Brassica and Arabidopsis facilitate study of this pervasive force in the evolution of all plants.     

The evolution of armament strength: evidence for a constraint on the biting performance of claws of durophagous decapods

Performance data for the claws of six sympatric species of Cancer crabs confirmed a puzzling pattern reported previously for two other decapod crustaceans (stone crabs, Menippe mercenaria, and lobsters, Homarus americanus): Although biting forces increased, maximum muscle stresses (force per unit area) declined with increasing claw size. The negative allometry of muscle stress and the stress at a given claw size were fairly consistent within and among Cancer species despite significant differences in adult body size and relative claw size, but were not consistent among decapod genera. Therefore, claw height can be used as a reliable predictor of maximum biting force for the genus Cancer, but must be used with caution as a predictor of maximum biting force in wider evolutionary and biogeographical comparisons of decapods. The decline in maximum muscle stress with increasing claw size in Cancer crabs contrasts with the pattern in several other claw traits. Significantly, three traits that affect maximal biting force increased intraspecifically with increasing claw size: relative claw size, mechanical advantage, and sarcomere length of the closer muscle. Closer apodeme area and angle of pinnation of the closer muscle fibers varied isometrically with claw size. The concordant behavior of these traits suggests selection for higher biting forces in larger crabs. The contrast between the size dependence of muscle stress (negative allometry) and the remaining claw traits (isometry or positive allometry) strongly suggests that an as yet unidentified constraint impairs muscle performance in larger claws. The negative allometry of muscle stress in two distantly related taxa (stone crabs and lobsters) further suggests this constraint may be widespread in decapod crustaceans. The implications of this performance constraint for the evolution of claw size and the "arms-race" between decapod predators and their hard-shelled prey is discussed.     

Predicting worldwide invasiveness for four major problematic decapods: an evaluation of using different calibration sets

Recently, there has been much debate whether niche based models (NBM) can predict biological invasions into new areas. These studies have chiefly focused on the type of occurrence data to use for model calibration. Additionally, pseudo‐absences are also known to cause uncertainty in NBM, but are rarely tested for predicting invasiveness. Here we test the implications of using different calibration sets for building worldwide invasiveness models for four major problematic decapods: Cherax destructor, Eriocheir sinensis, Pacifastacus leniusculus and Procambarus clarkii. Using Artificial Neural Networks models we compared predictions containing either native range occurrences (NRO), native and invasive occurrences (NIO) and invasive only (IRO) coupled with three types of pseudo‐absences – based on sampling only 1) the native range (NRA), 2) native and invasive ranges (NIA), and 3) worldwide random (WRA). We further analysed the potential gains in accuracy obtained through averaging across multiple models. Our results showed that NRO and IRO provided the best predictions for native and invaded ranges, respectively. Still, NIO provided the best balance in predicting both ranges. Pseudo‐absences had a large influence on the predictive performance of the models, and were more important for predictiveness than types of occurrences. Specifically, WRA performed the best and NRA and NIA performed poorly. We also found little benefit in combining predictions since best performing single‐models showed consistently higher accuracies. We conclude that NBM can provide useful information in forecasting invasiveness but are largely dependent on the type of initial information used and more efforts should be placed on recognizing its implications. Our results also show extensive areas which are highly suitable for the studied species worldwide. In total these areas reach from three to nine times the species current ranges and large portions of them are contiguous with currently invasive populations.