The evolutionary history of siphonophore tentilla: Novelties, convergence, and integration

Siphonophores are free-living predatory colonial hydrozoan cnidarians found in every region of the ocean. Siphonophore tentilla (tentacle side branches) are unique biological structures for prey capture, composed of a complex arrangement of cnidocytes (stinging cells) bearing different types of nematocysts (stinging capsules) and auxiliary structures. Tentilla present an extensive morphological and functional diversity across species. While associations between tentillum form and diet have been reported, the evolutionary history giving rise to this morphological diversity is largely unexplored. Here we examine the evolutionary gains and losses of novel tentillum substructures and nematocyst types on the most recent siphonophore phylogeny. Tentilla have a precisely coordinated high-speed strike mechanism of synchronous unwinding and nematocyst discharge. Here we characterize the kinematic diversity of this prey capture reaction using high-speed video and find relationships with morphological characters. Since tentillum discharge occurs in synchrony across a broad morphological diversity, we evaluate how phenotypic integration is maintaining character correlations across evolutionary time. We found that the tentillum morphospace has low dimensionality, identified instances of heterochrony and morphological convergence, and generated hypotheses on the diets of understudied siphonophore species. Our findings indicate that siphonophore tentilla are phenotypically integrated structures with a complex evolutionary history leading to a phylogenetically-structured diversity of forms which are predictive of kinematic performance and feeding habits.

Morphological variability of recent species of the order Cassiduloida (Echinodermata: Echinoidea) of Mexico

ntroduction: In Mexico, there are two recorded living species of Cassiduloida: Cassidulus caribaearum and Rhyncholampas pacifica. Most of the taxonomic studies on cassiduloids have used external morphology, pedicellariae and morphometric characters; however, the intraspecific variation of quantitative and qualitative characters has been poorly evaluated. Objective: To compare the basic morphology of R. pacifica and C. caribaearum. Methods: We examined a total of 2 158 specimens of R. pacifica and C. caribaearum, selecting 50 to evaluate shape and size with linear regression and Principal Component analysis. We selected an additional 62 specimens per species to identify significant character correlations and morphological groups within species. Results: There is a direct relationship between Test length and Test width. Test height/Test width, and Total length (oral view)/Distance from the ambitus to the peristome apex, are the two main ratios to distinguish both species. C. caribaearum is more dorsoventrally compressed and has a round peristome base; versus R. pacifica has a tall and triangular one. There are four morphological groups of C. caribaearum and two groups for R. pacifica. Conclusions: These two species can be distinguished with reliable morphological characters, in which peristome shape suggests that R. pacifica is more adapted to burrowing deeper into certain types of substratum.

Influence of different modes of morphological character correlation on phylogenetic tree inference

Phylogenetic analysis algorithms require the assumption of character independence - a condition generally acknowledged to be violated by morphological data. Correlation between characters can originate from intra-organismal features, shared phylogenetic history or forced by particular character-state coding schemes. Although the two first sources can be investigated by biologists a posteriori and the third one can be avoided a priori with good practices, phylogenetic software do not distinguish between any of them.In this study, we propose a new metric of raw character difference as a proxy for character correlation. Using thorough simulations, we test the effect of increasing or decreasing character differences on tree topology. Overall, we found an expected positive effect of reducing character correlations on recovering the correct topology. However, this effect is less important for matrices with a small number of taxa (25 in our simulations) where reducing character correlation is not more effective than randomly drawing characters. Furthermore, in bigger matrices (350 characters), there is a strong effect of the inference method with Bayesian trees being consistently less affected by character correlation than maximum parsimony trees.These results suggest that ignoring the problem of character correlation or independence can often impact topology in phylogenetic analysis. However, encouragingly, they also suggest that, unless correlation is actively maximised or minimised, probabilistic methods can easily accommodate for a random correlation between characters.

Evolution of Flowers, Pollination, and Plant Diversity

This chapter examines the evolution of flowers, pollination, and plant diversity. There is good evidence for pollinator-mediated selection and appropriate trait heritability in flowers, and there are well-established mechanisms by which this could bring about floral change, reproductive isolation, and evolutionary divergence or specialization. The chapter first considers the origin and early evolution of flowers before discussing the diversification of angiosperms. It then explores the advantages of animal pollination and goes on to discuss the extent to which pollination may have contributed to floral variation, plant speciation, and plant diversification. In particular, it explains whether pollinators select for floral divergence and describes five ways in which floral divergence could arise by selection: adaptation to distinct niches, character displacement, adaptive “wandering,” character correlations, and genetic drift.

Variation of morphological needle characters of Scots pine (Pinus sylvestris L.) populations in different habitats

We investigated the phenotypic variation of five morphological needle characters of Scots pine (<em>Pinus sylvestris</em> L.) in three populations. Two of the populations occurred in bogs and the third one formed a degraded fresh pine forest showing some features of a dry pine forest. The greatest variation was found in characters a (needle length), b and d, denoting the number of stomatal rows respectively on the convex and flat sides of the needle. Conversely, characters c and e (average number of stomata per 2 mm of needle length on the convex and the flat side of the needle) were stable, with little interindividual variation. The two bog populations and the dryland population exhibited different sets of character correlations. The interpopulation differentiational detected on the basis of morphological character expression was markedly influenced by both the different edaphic conditions, and the distinct genetic structure of the studied populations.

Differential vegetative and reproductive performances among fifteen guinea grass hybrids

The main scope of this work was to detect (Panicum maximum Jacq.) genotype differences as to morphoagronomic and seed quality indices, and to establish character correlations useful for determining vegetative and reproductive trends. Besides the flowering cycle, eight phenological and two seed quality traits were scored in a greenhouse randomized complete block experiment, as follows: plant height (PH), reproductive tiller number/overall tiller number (RTN/OTN), panicle number/reproductive tillers (PN/RT), leaf length (LL), leaf width (LW), panicle length (PL), fresh weight (FW), dry weight (DW), number of seeds/g (NS/G) and seed sample physical purity (SPP). Very-early and early-flowering hybrids consistently showed the highest correlation values among flowering cycle and RTN/OTN (r = -0.59**), PN/RT (r = -0.48**), NS/G (r = -0.88**) and SPP (r = -0.80**) (reproductive parameters) while intermediate and late-flowering hybrids presented the highest values for LL (r = 0.53**), LW (r = 0.60**), PL (r = 0.77**), FW (r = 0.78**) and DW (r = 0.85**) (vegetative traits). The implications of these results for plant breeding and forage management purposes are discussed.