Sperm are the most diverse of all animal cell types, and much of the diversity in sperm design is thought to reflect adaptations to the highly variable conditions under which sperm function and compete to achieve fertilization. Recent work has shown that these conditions often evolve rapidly as a consequence of multiple mating, suggesting a role for sexual selection and sexual conflict in the evolution of sperm design. However, very little of the striking diversity in sperm design is understood functionally, particularly in internally fertilizing organisms. We use phylogenetic comparative analyses covering 16 species of the hermaphroditic flatworm genus Macrostomum to show that a complex sperm design is associated with reciprocal mating and that this complexity is lost secondarily when hypodermic insemination-sperm injection through the epidermis-evolves. Specifically, the complex sperm design, which includes stiff lateral bristles, is likely a male persistence trait associated with sexual conflicts over the fate of received ejaculates and linked to female resistance traits, namely an intriguing postcopulatory sucking behavior and a thickened epithelium of the sperm-receiving organ. Our results suggest that the interactions between sperm donor, sperm, and sperm recipient can change drastically when hypodermic insemination evolves, involving convergent evolution of a needle-like copulatory organ, a simpler sperm design, and a simpler female genital morphology. Our study documents that a shift in the mating behavior may alter fundamentally the conditions under which sperm compete and thereby lead to a drastic change in sperm design.Platyhelminthes | sexually antagonistic coevolution | simultaneous hermaphrodite | sperm morphology | traumatic insemination P arker's (1-3) far-reaching extension of Darwin's (4) narrow focus on precopulatory mating interactions highlighted that sexual selection continues to operate after mating partners have agreed to mate and that considering postcopulatory sexual selection therefore is crucial to understand the evolution of many reproductive traits (5, 6). This insight has led to extensive research in evolutionary biology that focused on understanding the biology of sperm (7), the most diverse of all animal cell types (8,9). From this research emerged an apparent consensus that the diversity in sperm design-the strikingly variable ways of constructing a sperm-reflects the highly variable physiological and morphological environments in which sperm have to survive, function, and compete for fertilization (5,(10)(11)(12)(13)(14). Moreover, recent studies have documented clearly that these environments can evolve rapidly, probably because of coevolutionary interactions linked to multiple mating and the resulting sexual selection and sexual conflicts (15-21). However, the bewildering diversity in sperm design is poorly understood at the functional level, particularly in internally fertilizing organisms (9,12,22). A recent review on the evolution of sperm morphological diversity concluded...

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Novel molecular data are presented to resolve the long-standing issue of the non-monophyly of the elasmobranch-hosted tapeworm order Tetraphyllidea relative to the other acetabulate eucestode orders. Bayesian Inference analyses of various combinations of full ssrDNA, and full or partial lsrDNA (D1-D3), sequence data, which included 134 species representing 97 genera across the 15 eucestode orders, were conducted. New ssrDNA data were generated for 82 species, partial lsrDNA data for 53 species, and full lsrDNA data for 29 species. The monophyly of each of the elasmobranch-hosted orders Cathetocephalidea, Litobothriidea, Lecanicephalidea, and Rhinebothriidea was confirmed, as was the non-monophyly of the Tetraphyllidea. Two relatively stable groups of tetraphyllidean taxa emerged and are hereby designated as new orders. The Onchoproteocephalidea n. ord. is established to recognize the integrated nature of one undescribed and ten described genera of hook-bearing tetraphyllideans, previously of the family Onchobothriidae, with the members of the order Proteocephalidea. The Phyllobothriidea n. ord. is established for a subset of 12 non-hooked genera characterized by scoleces bearing four bothridia each with an anterior accessory sucker; most parasitise sharks and have been assigned to the Phyllobothriidae at one time or another. Tentative ordinal placements are suggested for 8 additional genera; placements for the remaining tetraphyllidean genera have not yet emerged. We propose these 17 genera remain in the "Tetraphyllidea". Among these, particularly labile across analyses were Anthobothrium, Megalonchos, Carpobothrium, Calliobothrium, and Caulobothrium. The unique association of Chimaerocestus with holocephalans, rather than with elasmobranchs, appears to represent a host-switching event. Both of the non-elasmobranch hosted clades of acetabulate cestodes (i.e., Proteocephalidea and Cyclophyllidea and their kin) appear to have had their origins with elasmobranch cestodes. Across analyses, the sister group to the clade of "terrestrial" cestode orders was found to be an elasmobranch-hosted genus; as was the sister to the Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts freshwater fish and tetrapod-hosted Proteocephalidea. Whilst further data are required to resolve outstanding nomenclatural and phylogenetic issues, the present analyses contribute significantly to an understanding of the evolutionary radiation of the entire Cestoda. Clearly, elasmobranch tapeworms comprise the backbone of cestode phylogeny.

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Background: Mitochondrial (mt) genomes represent a rich source of molecular markers for a range of applications, including population genetics, systematics, epidemiology and ecology. In the present study, we used 454 technology (or the GS20, massively parallel picolitre reactor platform) to determine the complete mt genome of Haemonchus contortus (Nematoda: Trichostrongylidae), a parasite of substantial agricultural, veterinary and economic significance. We validate this approach by comparison with mt sequences from publicly available expressed sequence tag (EST) and genomic survey sequence (GSS) data sets.

The phylogenetic relationships of representative species of the superfamily Lepocreadioidea were assessed using partial lsrDNA and nad1 sequences. Forty-two members of the family Lepocreadiidae, six putative members of the Enenteridae, six gyliauchenid species and one Gorgocephalidae, were studied along with 22 species representing 8 families. The Lepocreadioidea is found to be monophyletic, except for the two species of the putative enenterid genus Cadenatella, which are found to be only distantly related to the lepocreadioids. The Lepocreadioidea is formed of five clades in a polytomy, the Gorgocephalidae, a clade containing the Enenteridae and Gyliauchenidae, a small clade of atypical lepocreadiines and the deep-sea lepidapedine lepocreadiids, a small clade consisting of a freshwater form and a group of shallow-water putative lepidapedines and the final clade includes the remaining lepocreadiids. Thus, the generally accepted concept of the Lepocreadiidae is polyphyletic. The Enenteridae (minus Cadenatella) and the Gyliauchenidae are jointly and individually monophyletic, and are sister groups. The nad1 gene on its own places a deep-sea lepocreadiine with the deep-sea lepidapedines, whereas lsrDNA, combined sequences and morphology place this deep-sea lepocreadiine within a group of typical lepocreadiids. It could not be demonstrated that a significant proportion of sites in the nad1 gene evolved under positive selection; this anomalous relationship therefore remains unexplained. Most deep-sea species are in a monophyletic group, a few of which also occur in shallow waters, retaining some characters of the deep-sea clade. Many lepocreadioid species infect herbivorous fish, and it may be that the recently discovered life-cycle involving a bivalve first intermediate host and metacercariae encysted on vegetation is a common life-cycle pattern. The host relationships show no indication of co-speciation, although the host-spectrums exhibited are not random, with related worms tending to utilize related hosts. There are, however, many exceptions. Morphology is found to be of limited value in indicating higher level relationships. For example, even with the benefit of hindsight the gyliauchenids show little morphological similarity to their sister group, the Enenteridae.