Darwin's aliens

Making predictions about aliens is not an easy task. Much of the work that has been done has focused on extrapolating from empirical observations and mechanistic understanding of physics, chemistry, and biology. Another approach is to utilise theory to make predictions that are not tied to details of Earth. Here, we show how evolutionary theory can be used to make predictions about aliens. We argue that aliens will undergo natural selection – something that should not be taken for granted but that rests on firm theoretical grounds. Given aliens undergo natural selection, we can say something about their evolution. In particular, we can say something about how complexity will arise in space. Complexity has increased on Earth as a result of a handful of events, known as the major transitions in individuality. Major transitions occur when groups of individuals come together to form a new higher level of individual, such as when single celled organisms evolved into multicellular organisms. Both theory and empirical data suggest that extreme conditions are required for major transitions to occur. We suggest that major transitions are likely to be the route to complexity on other planets, and that we should expect them to have been favoured by similarly restrictive conditions. Thus, we can make specific predictions about the biological makeup of complex aliens

Do you see what I see? Optical morphology and visual capability of ‘disco’ clams ( Ctenoides ales

The ‘disco’ clam Ctenoides ales (Finlay, 1927) is a marine bivalve that has a unique, vivid flashing display that is a result of light scattering by silica nanospheres and rapid mantle movement. The eyes of C. ales were examined to determine their visual capabilities and whether the clams can see the flashing of conspecifics. Similar to the congener C. scaber, C. ales exhibits an off-response (shadow reflex) and an on-response (light reflex). In field observations, a shadow caused a significant increase in flash rate from a mean of 3.9 Hz to 4.7 Hz (P=0.0016). In laboratory trials, a looming stimulus, which increased light intensity, caused a significant increase in flash rate from a median of 1.8 Hz to 2.2 Hz (P=0.0001). Morphological analysis of the eyes of C. ales revealed coarsely-packed photoreceptors lacking sophisticated structure, resulting in visual resolution that is likely too low to detect the flashing of conspecifics. As the eyes of C. ales are incapable of perceiving conspecific flashing, it is likely that their vision is instead used to detect predators

Charting Evolution’s Trajectory: Using Molluscan Eye Diversity to Understand Parallel and Convergent Evolution

For over 100 years, molluscan eyes have been used as an example of convergent evolution and, more recently, as a textbook example of stepwise evolution of a complex lens eye via natural selection. Yet, little is known about the underlying mechanisms that create the eye and generate different morphologies. Assessing molluscan eye diversity and understanding how this diversity came about will be important to developing meaningful interpretations of evolutionary processes. This paper provides an introduction to the myriad of eye types found in molluscs, focusing on some of the more unusual structures. We discuss how molluscan eyes can be applied to the study of evolution by examining patterns of convergent and parallel evolution and provide several examples, including the putative convergence of the camera-type eyes of cephalopods and vertebrates

Patterns of Diversity in Soft-Bodied Meiofauna: Dispersal Ability and Body Size Matter

Background: Biogeographical and macroecological principles are derived from patterns of distribution in large organisms, whereas microscopic ones have often been considered uninteresting, because of their supposed wide distribution. Here, after reporting the results of an intensive faunistic survey of marine microscopic animals (meiofauna) in Northern Sardinia, we test for the effect of body size, dispersal ability, and habitat features on the patterns of distribution of several groups.Methodology/Principal Findings: As a dataset we use the results of a workshop held at La Maddalena (Sardinia, Italy) in September 2010, aimed at studying selected taxa of soft-bodied meiofauna (Acoela, Annelida, Gastrotricha, Nemertodermatida, Platyhelminthes and Rotifera), in conjunction with data on the same taxa obtained during a previous workshop hosted at Tjärnö (Western Sweden) in September 2007. Using linear mixed effects models and model averaging while accounting for sampling bias and potential pseudoreplication, we found evidence that: (1) meiofaunal groups with more restricted distribution are the ones with low dispersal potential; (2) meiofaunal groups with higher probability of finding new species for science are the ones with low dispersal potential; (3) the proportion of the global species pool of each meiofaunal group present in each area at the regional scale is negatively related to body size, and positively related to their occurrence in the endobenthic habitat.Conclusion/Significance: Our macroecological analysis of meiofauna, in the framework of the ubiquity hypothesis for microscopic organisms, indicates that not only body size but mostly dispersal ability and also occurrence in the endobenthic habitat are important correlates of diversity for these understudied animals, with different importance at different spatial scales. Furthermore, since the Western Mediterranean is one of the best-studied areas in the world, the large number of undescribed species (37%) highlights that the census of marine meiofauna is still very far from being complete

A silicified Early Triassic marine assemblage from Svalbard

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Species and diagnosis of the Families and Genera of Solenogastres (Mollusca)

Volume: 25Start Page: 73End Page: 14

The status of the Rhodopidae (Gastropoda: Euthyneura)

Volume: 32Start Page: 301End Page: 31

Les Cavibelonia (Mollusca, Solenogastres) d’Europe occidentale, avec description de deux nouvelles espèces

De nouveaux signalements de Solenogastres Cavibelonia des côtes françaises et espagnoles appartenant à la faune atlantique d’Europe occidentale, sont présentés. Cela comprend quatre espèces appartenant à différentes familles de l’ordre Cavibelonia. Deux d’entre elles sont nouvelles pour la science : Simrothiella vasconiensis n. sp. du sud-est du golfe de Gascogne et Alexandromenia gulaglandulata n. sp. du Bassin européen occidental. La découverte de Pararrhopalia pruvoti Simroth, 1893 au large de la Galice (Espagne) accroît considérablement son aire géographique, et la mention de Dorymenia sarsii (Koren &amp; Danielssen, 1877) du sud-est du golfe de Gascogne comble une lacune dans sa distribution. Ces signalements améliorent notre connaissance fragmentaire de la biodiversité des Solenogastres de la faune nord-est atlantique.New records of Solenogastres Cavibelonia from French and Spanish coasts, belonging to the West European Atlantic fauna, are presented. They include four species classified within different families of the order Cavibelonia. Two of them are new to science: Simrothiella vasconiensis n. sp. from the southeastern Bay of Biscay and Alexandromenia gulaglandulata n. sp. from the West European basin. The finding of Pararrhopalia pruvoti Simroth, 1893, from off Galicia (Spain) significantly enlarges its geographic range, and the record of Dorymenia sarsii (Koren &amp; Danielssen, 1877) from the southeastern Bay of Biscay bridges a former gap in distribution. These records improve our fragmented knowledge on the biodiversity of Solenogastres of the Northeast Atlantic fauna.</p

New Simrothiellidae (Mollusca : Solenogastres) from the Mozambique Channel, western Indian Ocean

Volume: 46Start Page: 252End Page: 26