Influences of phylogenetic position and fertilization biology on spermatozoal ultrastructure exemplified by exocoetoid and poeciliid fish

In a cladistic analysis, poeciliids and zenarchopterids homoplasically show elongation and flattening of the nucleus at right angles to the plane of the central axonemal singlets; in both the tip of the nucleus appears rounded in the plane of flattening but pointed in the plane at right angles. The two families differ in the distribution of mitochondria in the .elongate midpiece: circumferential in poeciliids but bilateral in zenarchopterids. In poeciliid sperm and independently in Zenarchopterus, the individual mitochondria are considerably more extensive circumferentially than longitudinally; they differ in poeciliids in being C-shaped. In Hemirhamphodon they are moderately elongate. In Dermogenys and Nomorhamphus they have been modified monophyletically as a pair of elongate mitochondrial derivatives. A wide cytoplasmic periaxonemal sheath (not seen in poeciliids) appears to have developed monophyletically in the ancestry of Hemirhamphodon, Dermogenys and Nomorhamphus with acquisition of radial rodlets only in Hemirhamphodon. A distinctive development in poeciliids is the submitochondrial net. Poeciliids have greatly reduced the axonemal fins which are a synapomorphy of the Actinopteri. Exocoetoids have retained well developed fins in Arrhamphus, Dermogenys and Nomorhamphus but reduction has occurred in Zenarchopterus, in which the fins are small, and, apparently independently, in Hemirhamphodon in which fins are absent. A posterior extension of the nucleus over the base of the axoneme is C-shaped and embraces almost the entire circumference of the axoneme in poeciliids but, independently developed, in zenarchopterids is a dorsal plate. Its absence in Hemirhamphodon is computed as a loss. These modifications relative to the aquasperm condition are deduced to have been occasioned by the adoption of internal fertilization. To what extent they are constrained by features of the genome peculiar to poeciliids, zenarchopterids or atherinomorphs or are demanded by minute differences in fertilization biology, or by a combination of the two, is not at present determinable.Abbreviations a: axoneme - as: central axonemal singlet microtubules - ad: axonemal doublets - cc: cytoplasmic canal (periaxonemal space) - cca: centriolar cap - dc: distal centriole - f: flagellum - fi: axonemal fin - m: mitochondrion - n: nucleus - nf: basal nuclear fossa - ps: peri-axonemal cytoplasmic sheath - s: dorsal spur of nucleus - sl: submitochondrial dense layer - sr: satellite rays     

Morphological structures for potential sperm storage in poeciliid fishes. Does superfetation matter?

Sperm storage within the female reproductive tract has been reported as a reproductive strategy in several species of vertebrates and invertebrates. However, the morphological structures that allow for sperm to be stored and kept viable for long periods are relatively unknown in osteichthyes. We use histological and stereological tools to identify and quantify sperm storage structures (spermathecae) in 12 species of viviparous Poeciliidae. We found spermathecae in nine species, six of which exhibit superfetation (the ability of females to simultaneously carry within the ovary two or more broods of embryos at different stages of development). These spermathecae are folds of ovarian tissue that close around spermatozoa. We compared the number and size (volume) of spermathecae between species with and without superfetation. Species that exhibit superfetation had a significantly higher number of spermathecae than species that do not exhibit this reproductive strategy. In addition, we found that the mean volume of spermathecae and total volume of spermathecae present in the ovary are marginally higher in species with superfetation. Our results contribute to the understanding of the morphological structures that allow for sperm storage in viviparous osteichthyes and suggest a positive relationship between superfetation and the capacity of females to store sperm.     

The probability of genetic parallelism and convergence in natural populations

Genomic and genetic methods allow investigation of how frequently the same genes are used by different populations during adaptive evolution, yielding insights into the predictability of evolution at the genetic level. We estimated the probability of gene reuse in parallel and convergent phenotypic evolution in nature using data from published studies. The estimates are surprisingly high, with mean probabilities of 0.32 for genetic mapping studies and 0.55 for candidate gene studies. The probability declines with increasing age of the common ancestor of compared taxa, from about 0.8 for young nodes to 0.1–0.4 for the oldest nodes in our study. Probability of gene reuse is higher when populations begin from the same ancestor (genetic parallelism) than when they begin from divergent ancestors (genetic convergence). Our estimates are broadly consistent with genomic estimates of gene reuse during repeated adaptation to similar environments, but most genomic studies lack data on phenotypic traits affected. Frequent reuse of the same genes during repeated phenotypic evolution suggests that strong biases and constraints affect adaptive evolution, resulting in changes at a relatively small subset of available genes. Declines in the probability of gene reuse with increasing age suggest that these biases diverge with time.     

How intelligent is a cephalopod? Lessons from comparative cognition

The soft-bodied cephalopods including octopus, cuttlefish, and squid are broadly considered to be the most cognitively advanced group of invertebrates. Previous research has demonstrated that these large-brained molluscs possess a suite of cognitive attributes that are comparable to those found in some vertebrates, including highly developed perception, learning, and memory abilities. Cephalopods are also renowned for performing sophisticated feats of flexible behaviour, which have led to claims of complex cognition such as causal reasoning, future planning, and mental attribution. Hypotheses to explain why complex cognition might have emerged in cephalopods suggest that a combination of predation, foraging, and competitive pressures are likely to have driven cognitive complexity in this group of animals. Currently, it is difficult to gauge the extent to which cephalopod behaviours are underpinned by complex cognition because many of the recent claims are largely based on anecdotal evidence. In this review, we provide a general overview of cephalopod cognition with a particular focus on the cognitive attributes that are thought to be prerequisites for more complex cognitive abilities. We then discuss different types of behavioural flexibility exhibited by cephalopods and, using examples from other taxa, highlight that behavioural flexibility could be explained by putatively simpler mechanisms. Consequently, behavioural flexibility should not be used as evidence of complex cognition. Fortunately, the field of comparative cognition centres on designing methods to pinpoint the underlying mechanisms that drive behaviours. To illustrate the utility of the methods developed in comparative cognition research, we provide a series of experimental designs aimed at distinguishing between complex cognition and simpler alternative explanations. Finally, we discuss the advantages of using cephalopods to develop a more comprehensive reconstruction of cognitive evolution.     

Vicariance, climate change, anatomy and phylogeny of Restionaceae

Cutler suggested almost 30 years ago that there was convergent evolution between African and Australian Restionaceae in the distinctive culm anatomical features of Restionaceae. This was based on his interpretation of the homologies of the anatomical features, and these are here tested against a 'supertrec' phylogeny, based on three separate phvlogenies. The first is based on morphology and includes all genera; the other two are based on molecular sequences from the chloroplast genome-, one covers the African genera, and the other tin-Australian genera. This analysis corroborates Cutler's interpretation of convergent evolution between African and Australian Restionaceae. However, it indicates that for the Australian genera, the evolutionary pathway of the culm anatomy is much more complex than originally thought. In the most likely scenario, the ancestral Restionaceae have protective cells derived from the chlorenchyma. These persist in African Restionaceae, but are soon lost in Australian Restionaceae. Pillar cells and sclerenchyma ribs evolve early in the diversification of Australian Restionaceae, but are secondarily lost numerous times. In some of the reduction cases, the result is a very simple culm anatomy, which Cutler had interpreted as a primitively simple culm type, while in other cases it appears as if the functions of the ribs and pillars may have been taken over by a new structure, protective cells developed from epidermal, rather than chlorenchyma, cells. Cutler suggested that this convergent evolution might have been in response to Tertiary climatic deterioration, but this study finds no strong corroborating evidence for this.     

Repeated modification of early limb morphogenesis programmes underlies the convergence of relative limb length in Anolis lizards

The independent evolution of similar morphologies has long been a subject of considerable interest to biologists. Does phenotypic convergence reflect the primacy of natural selection, or does development set the course of evolution by channelling variation in certain directions? Here, we examine the ontogenetic origins of relative limb length variation among Anolis lizard habitat specialists to address whether convergent phenotypes have arisen through convergent developmental trajectories. Despite the numerous developmental processes that could potentially contribute to variation in adult limb length, our analyses reveal that, in Anolis lizards, such variation is repeatedly the result of changes occurring very early in development, prior to formation of the cartilaginous long bone anlagen.