Cynthia Faux & Daniel J. Field (2017)
Distinct developmental pathways underlie independent losses of flight in ratites.
Biology Letters 13(7): 20170234
Recent phylogenetic studies question the monophyly of ratites (large, flightless birds incorporating ostriches, rheas, kiwis, emus and cassowaries), suggesting their paraphyly with respect to flying tinamous (Tinamidae). Flightlessness and large body size have thus likely evolved repeatedly among ratites, and separately in ostriches (Struthio) and emus (Dromaius). Here, we test this hypothesis with data from wing developmental trajectories in ostriches, emus, tinamous and chickens. We find the rate of ostrich embryonic wing growth falls within the range of variation exhibited by flying taxa (tinamous and chickens), but that of emus is extremely slow. These results indicate flightlessness was acquired by different developmental mechanisms in the ancestors of ostriches (peramorphosis) and the emu–cassowary clade (paedomorphosis), and corroborate the hypothesis that flight loss has evolved repeatedly among ratites.
Marcio R. Pie, Leonardo L. F. Campos, Andreas L. S. Meyer & Andressa Duran (2017)
The evolution of climatic niches in squamate reptiles.
Proceedings of the Royal Society B 284 20170268
Despite the remarkable diversity found in squamate reptiles, most of their species tend to be found in warm/dry environments, suggesting that climatic requirements played a crucial role in their diversification, yet little is known about the evolution of their climatic niches. In this study, we integrate climatic information associated with the geographical distribution of 1882 squamate species and their phylogenetic relationships to investigate the tempo and mode of climatic niche evolution in squamates, both over time and among lineages. We found that changes in climatic niche dynamics were pronounced over their recent squamate evolutionary history, and we identified extensive evidence for rate heterogeneity in squamate climatic niche evolution. Most rate shifts involved accelerations, particularly over the past 50 Myr. Most squamates occupy similar regions of the climatic niche space, with only a few lineages diversifying into colder and humid climatic conditions. The changes from arid to mesic conditions in some regions of the globe may have provided opportunities for climatic niche evolution, although most lineages tended to remain near their ancestral niche. Variation in rates of climatic niche evolution seems common, particularly in response to the availability of new climatic conditions over evolutionary time.
Robert E. Poelmann, Adriana C. Gittenberger-de Groot,Marcel W. M. Biermans,Anne I. Dolfing, Armand Jagessar, Sam van Hattum, Amanda Hoogenboom, Lambertus J. Wisse, Rebecca Vicente-Steijn, Merijn A. G. de Bakker, Freek J. Vonk, Tatsuya Hirasawa, Shigeru Kuratani & Michael K. Richardson (2017)
Outflow tract septation and the aortic arch system in reptiles: lessons for understanding the mammalian heart.
EvoDevo (2017) 8: 9.
Cardiac outflow tract patterning and cell contribution are studied using an evo-devo approach to reveal insight into the development of aorto-pulmonary septation.
We studied embryonic stages of reptile hearts (lizard, turtle and crocodile) and compared these to avian and mammalian development. Immunohistochemistry allowed us to indicate where the essential cell components in the outflow tract and aortic sac were deployed, more specifically endocardial, neural crest and second heart field cells. The neural crest-derived aorto-pulmonary septum separates the pulmonary trunk from both aortae in reptiles, presenting with a left visceral and a right systemic aorta arising from the unseptated ventricle. Second heart field-derived cells function as flow dividers between both aortae and between the two pulmonary arteries. In birds, the left visceral aorta disappears early in development, while the right systemic aorta persists. This leads to a fusion of the aorto-pulmonary septum and the aortic flow divider (second heart field population) forming an avian aorto-pulmonary septal complex. In mammals, there is also a second heart field-derived aortic flow divider, albeit at a more distal site, while the aorto-pulmonary septum separates the aortic trunk from the pulmonary trunk. As in birds there is fusion with second heart field-derived cells albeit from the pulmonary flow divider as the right 6th pharyngeal arch artery disappears, resulting in a mammalian aorto-pulmonary septal complex. In crocodiles, birds and mammals, the main septal and parietal endocardial cushions receive neural crest cells that are functional in fusion and myocardialization of the outflow tract septum. Longer-lasting septation in crocodiles demonstrates a heterochrony in development. In other reptiles with no indication of incursion of neural crest cells, there is either no myocardialized outflow tract septum (lizard) or it is vestigial (turtle). Crocodiles are unique in bearing a central shunt, the foramen of Panizza, between the roots of both aortae. Finally, the soft-shell turtle investigated here exhibits a spongy histology of the developing carotid arteries supposedly related to regulation of blood flow during pharyngeal excretion in this species.
This is the first time that is shown that an interplay of second heart field-derived flow dividers with a neural crest-derived cell population is a variable but common, denominator across all species studied for vascular patterning and outflow tract septation. The observed differences in normal development of reptiles may have impact on the understanding of development of human congenital outflow tract malformations.
Edwin R. Price, Tushar S. Sirsat, Sarah K.G. Sirsat, Gurdeep Kang, Jantana Keereetaweep, Mina Aziz, Kent D. Chapman & Edward M. Dzialowski (2017)
Thermal acclimation in American alligators: Effects of temperature regime on growth rate, mitochondrial function, and membrane composition.
Journal of Thermal Biology 68(A): 45-54
We examine effects of temperature on growth and mitochondrial function in alligators.
Highest growth rate was achieved by animals cycled between warm and cold.
Mitochondrial function was not affected by temperature regime.
In brain membranes, headgroups but not fatty acid composition was altered.
Liver mitochondria had elevated DHA in cold alligators.
We investigated the ability of juvenile American alligators (Alligator mississippiensis) to acclimate to temperature with respect to growth rate. We hypothesized that alligators would acclimate to cold temperature by increasing the metabolic capacity of skeletal muscles and the heart. Additionally, we hypothesized that lipid membranes in the thigh muscle and liver would respond to low temperature, either to maintain fluidity (via increased unsaturation) or to maintain enzyme reaction rates (via increased docosahexaenoic acid). Alligators were assigned to one of 3 temperature regimes beginning at 9 mo of age: constant warm (30 °C), constant cold (20 °C), and daily cycling for 12 h at each temperature. Growth rate over the following 7 mo was highest in the cycling group, which we suggest occurred via high digestive function or feeding activity during warm periods and energy-saving during cold periods. The warm group also grew faster than the cold group. Heart and liver masses were proportional to body mass, while kidney was proportionately larger in the cold group compared to the warm animals. Whole-animal metabolic rate was higher in the warm and cycling groups compared to the cold group – even when controlling for body mass – when assayed at 30 °C, but not at 20 °C. Mitochondrial oxidative phosphorylation capacity in permeabilized fibers of thigh muscle and heart did not differ among treatments. Membrane fatty acid composition of the brain was largely unaffected by temperature treatment, but adjustments were made in the phospholipid headgroup composition that are consistent with homeoviscous adaptation. Thigh muscle cell membranes had elevated polyunsaturated fatty acids in the cold group relative to the cycling group, but this was not the case for thigh muscle mitochondrial membranes. Liver mitochondria from cold alligators had elevated docosahexaenoic acid, which might be important for maintenance of reaction rates of membrane-bound enzymes.
Marta Vidal-García and J. Scott Keogh (2017)
Phylogenetic conservatism in skulls and evolutionary lability in limbs – morphological evolution across an ancient frog radiation is shaped by diet, locomotion and burrowing.
BMC Evolutionary Biology (2017) 17: 165
Quantifying morphological diversity across taxa can provide valuable insight into evolutionary processes, yet its complexities can make it difficult to identify appropriate units for evaluation. One of the challenges in this field is identifying the processes that drive morphological evolution, especially when accounting for shape diversification across multiple structures. Differential levels of co-varying phenotypic diversification can conceal selective pressures on traits due to morphological integration or modular shape evolution of different structures, where morphological evolution of different modules is explained either by co-variation between them or by independent evolution, respectively.
Here we used a 3D geometric morphometric approach with x-ray micro CT scan data of the skull and bones of forelimbs and hindlimbs of representative species from all 21 genera of the ancient Australo-Papuan myobatrachid frogs and analysed their shape both as a set of distinct modules and as a multi-modular integrative structure. We then tested three main questions: (i) are evolutionary patterns and the amount and direction of morphological changes similar in different structures and subfamilies?, (ii) do skulls and limbs show different levels of integration?, and (iii) is morphological diversity of skulls and limbs shaped by diet, locomotion, burrowing behavior, and ecology?.
Our results in both skulls and limbs support a complex evolutionary pattern typical of an adaptive radiation with an early burst of phenotypic variation followed by slower rates of morphological change. Skull shape diversity was phylogenetically conserved and correlated with diet whereas limb shape was more labile and associated with diet, locomotion, and burrowing behaviour. Morphological changes between different limb bones were highly correlated, depicting high morphological integration. In contrast, overall limb and skull shape displayed semi-independence in morphological evolution, indicating modularity.
Our results illustrate how morphological diversification in animal clades can follow complex processes, entailing selective pressures from the environment as well as multiple trait covariance with varying degrees of independence across different structures. We suggest that accurately quantifying shape diversity across multiple structures is crucial in order to understand complex evolutionary processes.