The adaptor hypothesis revisited

As originally postulated in Crick's Adaptor hypothesis, the faithful synthesis of proteins from messenger RNA is dependent on the presence of perfectly acylated tRNAs. The hypothesis also suggested that each aminoacyl-tRNA would be made by a unique enzyme. Recent data have now forced a revision of this latter point, with an increasingly diverse array of enzymes and pathways being implicated in aminoacyl-tRNA synthesis. These unexpected findings have far-reaching implications for our understanding of protein synthesis and its origins.     

Teams in animal societies

We review the existence of teams in animal societies. Teamshave previously been dismissed in all but a tiny minority ofinsect societies. "Team" is a term not generally used in studiesof vertebrates. We propose a new rigorous definition of a teamthat may be applied to both vertebrate and invertebrate societies.We reconsider what it means to work as a team or group andsuggest that there are many more teams in insect societies than previously thought. A team task requires different subtasksto be performed concurrently for successful completion. Thereis a division of labor within a team. Contrary to previousreviews of teams in social insects, we do not constrain teamsto consist of members of different castes and argue that teammembers may be interchangeable. Consequently, we suggest thata team is simply the set of individuals that performs a teamtask. We contrast teams with groups and suggest that a grouptask requires the simultaneous performance and cooperationof two or more individuals for successful completion. In agroup, there is no division of labor—each individual performs the same task. We also contrast vertebrate and invertebrateteams and find that vertebrate teams tend to be associatedwith hunting and are based on individual recognition. Invertebrateteams occur in societies characterized by a great deal of redundancy,and we predict that teams in insect societies are more likelyto be found in large polymorphic ("complex") societies thanin small monomorphic ("simple") societies.     

The new head hypothesis revisited

In 1983, a new theory, the New Head Hypothesis, was generated within the context of the Tunicate Hypothesis of deuterostome evolution. The New Head Hypothesis comprised four claims: (1) neural crest, neurogenic placodes, and muscularized hypomere are unique to vertebrates, (2) the structures derived from these tissues allowed a shift from filter feeding to active predation, (3) the rostral head of vertebrates is a neomorphic unit, and (4) neural crest and neurogenic placodes evolved from the epidermal nerve plexus of ancestral deuterostomes. These claims are re-examined within the context of evolutionary developmental biology. The first may or may not be valid, depending on whether protochordates have these tissues in rudimentary form. Regarding the second, clearly, the elaboration of these tissues in vertebrates is correlated with a shift from filter feeding to active predation. The third claim is clarified, i.e., that the elaboration of the alar portion of the rostral brain and the development of olfactory organs and their associated connective tissues represent a neomorphic unit, which appears to be valid. The fourth is rejected. When the origin of neural crest and neurogenic placodes is examined within the context of developmental biology, it appears they evolved due to the rearrangement of germ layers in the blastulae of the deuterostomes that gave rise to chordates. Deuterostome evolution and the origin of vertebrates are also re-examined in the context of new data from developmental biology and taxonomy. The Tunicate Hypothesis is rejected, and a new version of the Dipleurula Hypothesis is presented.     

The hydraulic limitation hypothesis revisited

We proposed the hydraulic limitation hypothesis (HLH) as a mechanism to explain universal patterns in tree height, and tree and stand biomass growth: height growth slows down as trees grow taller, maximum height is lower for trees of the same species on resource-poor sites and annual wood production declines after canopy closure for even-aged forests. Our review of 51 studies that measured one or more of the components necessary for testing the hypothesis showed that taller trees differ physiologically from shorter, younger trees. Stomatal conductance to water vapour (g(s)), photosynthesis (A) and leaf-specific hydraulic conductance (K L) are often, but not always, lower in taller trees. Additionally, leaf mass per area is often greater in taller trees, and leaf area:sapwood area ratio changes with tree height. We conclude that hydraulic limitation of gas exchange with increasing tree size is common, but not universal. Where hydraulic limitations to A do occur, no evidence supports the original expectation that hydraulic limitation of carbon assimilation is sufficient to explain observed declines in wood production. Any limit to height or height growth does not appear to be related to the so-called age-related decline in wood production of forests after canopy closure. Future work on this problem should explicitly link leaf or canopy gas exchange with tree and stand growth, and consider a more fundamental assumption: whether tree biomass growth is limited by carbon availability.     

Dominance, aggression and reproduction in primate societies

Dominance relationships in primate societies are generally inferred by analyses of agonistic interactions. This aspect of social organization is so striking in macaque and baboon societies that many theoreticians have postulated selective mechanisms operating on the genetic attributes which contribute to high dominance rank. Alpha males were hypothesized to increase their genetic fitness by successfully competing with other males for access to ovulating females.Evidence relevant to these speculations has been mixed. Whereas some investigators found alpha males had near exclusive sexual access to females, others failed to confirm preferential access to ovulating females. Indeed, considerable variability in competition for females existed not only among species, but also among troops of the same species living in different habitats. Further, partner selection was not an exclusive male prerogative; females proved to express active preferences for particular males as sexual partners, and these preferences were not related to high male aggressivity.Alpha males, however, were noted to maintain their positions through social skills as members of a central core or alliance, and high rank was related primarily to seniority. Moreover, alpha males responded actively to challenges to the troop and were judged to contribute significantly to the survival of infants. It was therefore hypothesized that increased genetic fitness related to the increased survival of immature animals in the troop, most of which would already be the offspring of senior (and hence alpha) males. Selection would then be for the social skills leading to successful alliances in troop defense. Such skills might also relate to female partner preferences thus increasing the reproductive effectiveness of alpha males at any point in their careers, including years prior to and following their assumption of alpha rank.     

The Alpine Fault biogeographic hypothesis revisited

The New Zealand Alpine Fault is a major tectonic feature located on the mutual boundary of the Australian and Pacific Plates which is hypothesized to have undergone some 470 km of right‐lateral displacement. The Nelson and Westland provinces have moved north‐east relative to the rest of the South Island. Many plant and animal taxa show a conspicuous distribution gap in the central South Island, and traditionally this has been explained by glacial extirpation of the central populations. However, the gap is usually filled by a closely related taxon. Furthermore, the taxa involved occupy a wide ecological range, and include intertidal algae, shorefishes, lowland trees, and alpine herbs and insects that thrive around glaciers. The Alpine Fault biogeographic hypothesis [ Heads, M., 1998a . Biogeographic disjunction along the Alpine Fault, New Zealand. Biol. J. Linn. Soc. 63, 161–176; Heads, M., 1998b. Coprosma decurva (Rubiaceae), a new species from New Zealand. NZ J. Bot. 36, 65–69.], based on track and phylogenetic analyses, proposes that the disjunction has instead been caused by movement on the fault pulling apart plant and animal populations. Wallis and Trewick (2001 ) [ Wallis, G.P., Trewick, S.A., 2001 . Finding fault with vicariance: a critique of Heads (1998). Syst. Biol. 50, 602–609.] provided a critique of this idea and pointed out what they felt were nine problems with it. These problems are answered here and shown to result from Wallis and Trewick's misunderstanding of aspects of geology and biology involved in the hypothesis. In particular, they have confused the age of inception of the fault with the age of movement along it, and, by neglecting the related central taxa in the “gap”, have assumed the biogeographic hypothesis to be an uninformative two‐area statement, whereas in fact it is an informative three‐ or four‐area statement.     

The stromatoporoid animal revisited: Building the skeleton

Modern coralline sponges secrete a skeleton by means of a basal pinacoderm, intracellularly, or inside the soft tissue on an organic matrix The examination of terminal growth surfaces of stromatoporoids indicates that soft tissue in laminate and amalgamate forms occupied the upper galleries and that the skeletal elements were secreted within the soft tissue on an organic matrix. The stromatoporellids and clathrodictyids secreted the skeleton in modules that are homologous to the chambers of a sphinctozoan. In stromatoporellids the module was bounded by a floor that formed the upper layer of the tripatite lamina below and a roof that became the lower layer of the next lamina; it further included the intervening pillars. In clathrodictyids the module had only a roof and pillars, and the laminae are single layers. other stromatoporoids may have secreted their skeletons at the base of the soft tissue and had minimal occupation of the skeleton. *** Stromatoporoid, sphinctozoa, sclerospongiae, sponge, paleobiology.     

Partitioning of reproduction in animal societies

A key feature differentiating cooperative animal societies Is the apportionment of reproduction among individuals. Only recently have studies started to focus on intraspecific variability in the distribution of reproduction within animal societies, and the available data suggest that this variability might be greater than previously suspected. How can one account for intra-and interspecific variability in partitioning of reproduction? This Is one of the most intriguing problems in the study of social behaviour, and understanding the factors underlying this variability is one of the keys to understanding the properties of complex animal societies.     

Longevity suppresses conflict in animal societies

Models of social conflict in animal societies generally assume that within-group conflict reduces the value of a communal resource. For many animals, however, the primary cost of conflict is increased mortality. We develop a simple inclusive fitness model of social conflict that takes this cost into account. We show that longevity substantially reduces the level of within-group conflict, which can lead to the evolution of peaceful animal societies if relatedness among group members is high. By contrast, peaceful outcomes are never possible in models where the primary cost of social conflict is resource depletion. Incorporating mortality costs into models of social conflict can explain why many animal societies are so remarkably peaceful despite great potential for conflict.     

Hurricanes and coral reefs: The intermediate disturbance hypothesis revisited

A review of research on the effects of hurricanes on coral reefs suggests that the intermediate disturbance hypothesis may be applicable to shallow reef zones dominated by branching or foliaceous coral species that are especially susceptible to mechanical damage from storms. Diversity (H') increases because of an increase in evenness following destruction or removal of the species that was monopolizing the space. The intermediate disturbance hypothesis as presented by Connell focuses on changes in number of species, but should be expanded to include diversity (H') and evenness. It should also be modified to incorporate changes in living cover and the time elapsed since disturbances of varying intensities. This hypothesis predicts that when cover is high, diversity will be low. However, research on coral reefs does not consistently demonstrate an inverse correlation of coral diversity, and coral cover. An increase in cover and decrease in diversity with depth would also be expected because deeper reef zones generally experience less disturbance. However, higher diversity (both H' and species richness) is often associated with deeper zones. The effects of hurricanes on coral reefs will depend on the temporal and spatial scales under consideration, the life history characteristics and morphology of the dominant species, the depth of the reef zone, the ecological history of the site, and the influence of any additional natural or human stresses.     

The serial transformation hypothesis of vertebrate origins: comment on "The new head hypothesis revisited"

In "The New Head Hypothesis Revisited," R.G. Northcutt (2005. J Exp Zool (Mol Dev Evol) 304B:274-297) evaluates the original postulates of this hypothesis (Northcutt and Gans, 1983. Quart Rev Biol 58:1-28). One of these postulates is that the brain-particularly the forebrain-evolved at essentially the same time as many neural crest and neurogenic placode derivatives-including sensory ganglia, dermal skeleton and sensory capsules of the head, and branchial arches. Northcutt's subsequent paper in 1996 concluded with the idea that transitional forms might not have occurred at the origin of vertebrates. Butler proposed a "Serial Transformation" hypothesis in 2000, which disputed the latter idea in that paired eyes and an enlarged brain (but lacking telencephalon) were envisioned to have been gained before elaboration of most neural crest and neurogenic placodal derivatives. In 2003, J. Mallatt and J.-Y. Chen analyzed fossils of the Cambrian animal Haikouella, which strongly support its affinity to craniates and aspects of several hypotheses, including Butler's transformational model, because although branchial bars are present, most other neural crest and placodal derivatives are absent, while paired eyes and an enlarged brain (but probably without telencephalon) are present. A more complete picture of vertebrate origins can be realized when the various hypotheses are constructively reconciled.     

Social complexity and kinship in animal societies

Studies of eusocial invertebrates regard complex societies as those where there is a clear division of labour and extensive cooperation between breeders and helpers. In contrast, studies of social mammals identify complex societies as those where differentiated social relationships influence access to resources and reproductive opportunities. We show here that, while traits associated with social complexity of the first kind occur in social mammals that live in groups composed of close relatives, traits associated with the complexity of social relationships occur where average kinship between female group members is low. These differences in the form of social complexity appear to be associated with variation in brain size and probably reflect contrasts in the extent of conflicts of interest between group members. Our results emphasise the limitations of any unitary concept of social complexity and show that variation in average kinship between group members has far‐reaching consequences for animal societies.