MORPHOLOGICAL EVOLUTION MEDIATED BY BEHAVIOR IN THE DAMSELFLIES OF TWO COMMUNITIES

Behavior can play a mediating role in determining the selective pressures that influence the evolution of morphological structures. To examine this, I quantified patterns of morphological variation among larvae of Enallagma damselfly species (Odonata: Coenagrionidae) that use different behaviors to avoid the major predators found in each of two communities, lakes with and without fish. Specifically, I quantified the sizes and shapes of the abdomens and caudal lamellae (used for swimming) and legs for three species from fishless lakes and six species from lakes with fish. A preliminary cladistic analysis indicates that species within each lake type are not members of a single clade, which supports the conclusions of previous odonate taxonomists. Previous studies have shown that species in fishless lakes are very active, running and swimming frequently and at high rates of speed in the absence of predators, and they avoid their primary predators, large dragonflies, by swimming. These species have the widest abdomens, the largest caudal lamellae relative to overall body size, and the longest legs of the species studied, which should make them powerful swimmers and runners. Furthermore, species in fishless lakes are morphologically very similar to one another and differ greatly from fish-lake species, although each is more closely related to species in fish lakes. In contrast, species from lakes with fish move very slowly and infrequently in the absence of predators and do not attempt to evade attacking predators. However, despite their behavioral similarity, large interspecific variation in morphology exists among the fish-lake species, and the only morphological patterns were differences associated with membership in the two primary clades identified in the cladistic analysis. A modification of Felsenstein's (1985) method of evolutionary contrasts which allows character change to be isolated along single branches is introduced and is used to reconstruct the evolutionary histories of these characters. This analysis suggests that large increases in caudal lamella size, abdominal segment lengths and widths, and leg length accompany speciation events associated with habitat shifts from fish-lakes to fishless lakes. Following habitat shifts selection pressures exerted by dragonfly predation apparently favored swimming as an escape tactic, which mediated selection pressures onto morphologies used in swimming to increase swimming performance; morphological patterns in extant species reflect this adaptation to a new environment. Mechanisms by which behaviorally mediated selection could have accelerated evolutionary dynamics following founder events are discussed.     

The correlated evolution of three-dimensional reproductive structures between male and female damselflies

For many taxa, species are defined by the morphologies of reproductive structures. In many odonates, these structures are the cerci of males (used to hold females during mating) and the thoracic plates of females where the male cerci contact the females' bodies. A previous study showed that the shapes of cerci of Enallagma males (Zygoptera: Coenagrionidae) are best explained by an evolutionary model of punctuated change at the time of speciation, with a homogeneous rate of change across the entire phylogeny of the genus. In the present study, we examine the evolution of shape change in the corresponding female plates. We found that, like male cerci, the shapes of Enallagma female thoracic plates could best be explained by an evolutionary model of punctuated change at the time of speciation, with a homogeneous rate of change across the clade. Moreover, the evolutionary contrasts quantifying the rates of change in male cerci and female thoracic plates were positively related across the history of the clade, demonstrating that these male and female structures evolve in a correlated fashion. This pattern of evolution suggests that these structures are primary signals of species identity during mating.     

MORPHOLOGICAL VARIABILITIES OF THREE CLOSELY RELATED MATING GROUPS OF CLOSTERIUM EHRENBERGII MENEGHINI (CHLOROPHYTA)1

The ranges of morphological variabilities in vegetative cells of three closely related mating groups of Closterium ehrenbergii Meneghini were statistically analyzed, having been grown under standard and uniform culture conditions, using Group A clones from Japan and Australia, Group B clones from Japan and Taiwan and Group H clones from Nepal. Significant differences in the morphological characters were not recognized between the two complementary mating types in any of the three groups. It has been shown that cells of Group A are smallest (mean width 50 μm and mean length 250 μm) and cells of Group B are largest (mean width 67 μm and mean length 404 μm), while cells of Group H are intermediate (mean width 57 μm and mean length 333 μm). There are considerable differences in the mean cell size between the three mating groups, although some intergrading clones were recognized. Degrees of the intergrading overlap were shown to be small between the sympatric groups (A and B) and large between the two pairs of allopatric groups (A and H & B and H). It has been shown that cells of Group A are shorter and much more curved than cells of the other two mating groups. Cells of Groups B and H are slender and less curved. It has also been shown that the ranges in cell size of each mating group are smaller than those currently accepted for C. ehrenbergii.     

Effectiveness of modern leaf analysis tools for the morpho‐ecological study of plants: the case of Primula albenensis

Scientific and technological progress has led to the creation of analysis tools that have revolutionized traditional studies in morphology and plant ecology. Recently developed methods and tools which, on the basis of leaf samples, allow for geometric morphometric analyses and the evaluation of functional strategies are good examples. These methods, still little used, have never been applied on leaf samples to simultaneously obtain information on their morphometry and the ecology of the plants. This article discusses the effectiveness of modern leaf analysis tools for geometric morphometrics (outline analysis) and studies of functional strategies based on the competitor‐stress tolerator‐ruderal (CSR) scheme, using a study of a steno‐endemic plant of the Alps, Primula albenensis Banfi et Ferl. as an example. These aspects were analyzed using leaf samples collected in the only two areas where this species grows. CSR analyses revealed that P. albenensis is not a stress‐tolerant species (C:S:R = 37:1:62), as previously thought. Moreover, no significant intraspecific differences in functional strategy were revealed. Instead, outline analysis highlighted a significant difference (p < 0.001) between leaves collected from the two sampling areas. The results of this study and others reported in the literature therefore suggest that these modern methods of leaf analysis are cheap, effective and relatively simple to perform. Furthermore, researchers are able to carry out geometric morphometric and CSR analysis using the same samples of leaves in order to maximize the information content provided by the analysis of a plant material which may not be easily available.     

Shape analysis of two sympatric coral species: Implications for taxonomy and evolution

Fourier shape analysis of Pleurodictyum americanum and P. dividua , favositid tabulate corals, from the Middle Devonian Hamilton Group of New York State, indicates that colony growth form is variable within species between environments, but that the range of variability in growth form is static through time. Pleurpdictyum dividua displays a columnar morphotype; however, P. dividua and P. americanum cannot be discriminated from one another based on colony shape alone. A major prediction of the punctuated equilibrium model of evolution is morphological stasis throughout the duration of a species. Harmonic means of assemblages of P. americanum show no persistent temporal trends. The range of harmonic means present among the oldest assemblages (Centerfield Limestone) are comparable to those among the youngest assemblages (Windom Shale) and to those in the intervening intervals. Character stasis in colony growth form lasted throughout a 2.5-3.5 my interval. In tabulate corals, where reproductive modes such as fragmentation have not been demonstrated, growth form may be useful in interpreting ancient environments. In addition, the tempo of evolution of growth form can be analyzed when sufficient morphological data are available from a wide distribution of environments. Thus, Fourier shape analysis of growth form provides a powerful tool for paleontologists to interpret the ecology and evolution of colonial marine animals.