Lack of Signal for the Impact of Conotoxin Gene Diversity on Speciation Rates in Cone Snails.

Understanding why some groups of organisms are more diverse than others is a central goal in macroevolution. Evolvability, or the intrinsic capacity of lineages for evolutionary change, is thought to influence disparities in species diversity across taxa. Over macroevolutionary time scales, clades that exhibit high evolvability are expected to have higher speciation rates. Cone snails (family: Conidae, $>$900 spp.) provide a unique opportunity to test this prediction because their toxin genes can be used to characterize differences in evolvability between clades. Cone snails are carnivorous, use prey-specific venom (conotoxins) to capture prey, and the genes that encode venom are known and diversify through gene duplication. Theory predicts that higher gene diversity confers a greater potential to generate novel phenotypes for specialization and adaptation. Therefore, if conotoxin gene diversity gives rise to varying levels of evolvability, conotoxin gene diversity should be coupled with macroevolutionary speciation rates. We applied exon capture techniques to recover phylogenetic markers and conotoxin loci across 314 species, the largest venom discovery effort in a single study. We paired a reconstructed timetree using 12 fossil calibrations with species-specific estimates of conotoxin gene diversity and used trait-dependent diversification methods to test the impact of evolvability on diversification patterns. Surprisingly, we did not detect any signal for the relationship between conotoxin gene diversity and speciation rates, suggesting that venom evolution may not be the rate-limiting factor controlling diversification dynamics in Conidae. Comparative analyses showed some signal for the impact of diet and larval dispersal strategy on diversification patterns, though detection of a signal depended on the dataset and the method. If our results remain true with increased taxonomic sampling in future studies, they suggest that the rapid evolution of conid venom may cause other factors to become more critical to diversification, such as ecological opportunity or traits that promote isolation among lineages.

Glowing seashells: diversity of fossilized coloration patterns on coral reef-associated cone snail (Gastropoda: Conidae) shells from the Neogene of the Dominican Republic.

The biology of modern Conidae (cone snails)--which includes the hyperdiverse genus Conus--has been intensively studied, but the fossil record of the clade remains poorly understood, particularly within an evolutionary framework. Here, ultraviolet light is used to reveal and characterize the original shell coloration patterns of 28 species of cone snails from three Neogene coral reef-associated deposits from the Cibao Valley, northern Dominican Republic. These fossils come from the upper Miocene Cercado Fm. and lower Pliocene Gurabo Fm., and range in age from about 6.6-4.8 Ma. Comparison of the revealed coloration patterns with those of extant species allow the taxa to be assigned to three genera of cone snails (Profundiconus, Conasprella, and Conus) and at least nine subgenera. Thirteen members of these phylogenetically diverse reef faunas are described as new species. These include: Profundiconus? hennigi, Conasprella (Ximeniconus) ageri, Conus anningae, Conus lyelli, Conus (Atlanticonus?) franklinae, Conus (Stephanoconus) gouldi, Conus (Stephanoconus) bellacoensis, Conus (Ductoconus) cashi, Conus (Dauciconus) garrisoni, Conus (Dauciconus?) zambaensis, Conus (Spuriconus?) kaesleri, Conus (Spuriconus?) lombardii, and Conus (Lautoconus?) carlottae. Each of the three reef deposits contain a minimum of 14-16 cone snail species, levels of diversity that are similar to modern Indo-Pacific reef systems. Finally, most of the 28 species can be assigned to modern clades and thus have important implications for understanding the biogeographic and temporal histories of these clades in tropical America.

Geometric morphometric character suites as phylogenetic data: extracting phylogenetic signal from gastropod shells.

Despite being the objects of numerous macroevolutionary studies, many of the best represented constituents of the fossil record-including diverse examples such as foraminifera, brachiopods, and mollusks-have mineralized skeletons with limited discrete characteristics, making morphological phylogenies difficult to construct. In contrast to their paucity of phylogenetic characters, the mineralized structures (tests and shells) of these fossil groups frequently have distinctive shapes that have long proved useful for their classification. The recent introduction of methodologies for including continuous data directly in a phylogenetic analysis has increased the number of available characters, making it possible to produce phylogenies based, in whole or part, on continuous character data collected from such taxa. Geometric morphometric methods provide tools for accurately characterizing shape variation and can produce quantitative data that can therefore now be included in a phylogenetic matrix in a nonarbitrary manner. Here, the marine gastropod genus Conus is used to evaluate the ability of continuous characters-generated from a geometric morphometric analysis of shell shape-to contribute to a total evidence phylogenetic hypothesis constructed using molecular and morphological data. Furthermore, the ability of continuous characters derived from geometric morphometric analyses to place fossil taxa with limited discrete characters into a phylogeny with their extant relatives was tested by simulating the inclusion of fossil taxa. This was done by removing the molecular partition of individual extant species to produce a "cladistic pseudofossil" with only the geometric morphometric derived characters coded. The phylogenetic position of each cladistic pseudofossil taxon was then compared with its placement in the total evidence tree and a symmetric resampling tree to evaluate the degree to which morphometric characters alone can correctly place simulated fossil species. In 33-45% of the test cases (depending upon the approach used for measuring success), it was possible to place the pseudofossil taxon into the correct regions of the phylogeny using only the morphometric characters. This suggests that the incorporation of extinct Conus taxa into phylogenetic hypotheses will be possible, permitting a wide range of macroevolutionary questions to be addressed within this genus. This methodology also has potential to contribute to phylogenetic reconstructions for other major components of the fossil record that lack numerous discrete characters.

Exceptionally preserved jellyfishes from the Middle Cambrian.

Cnidarians represent an early diverging animal group and thus insight into their origin and diversification is key to understanding metazoan evolution. Further, cnidarian jellyfish comprise an important component of modern marine planktonic ecosystems. Here we report on exceptionally preserved cnidarian jellyfish fossils from the Middle Cambrian (approximately 505 million years old) Marjum Formation of Utah. These are the first described Cambrian jellyfish fossils to display exquisite preservation of soft part anatomy including detailed features of structures interpreted as trailing tentacles and subumbrellar and exumbrellar surfaces. If the interpretation of these preserved characters is correct, their presence is diagnostic of modern jellyfish taxa. These new discoveries may provide insight into the scope of cnidarian diversity shortly after the Cambrian radiation, and would reinforce the notion that important taxonomic components of the modern planktonic realm were in place by the Cambrian period.

A method for constraining the age of origination of derived characters.

Fossils are the physical records of the history of morphological character evolution on Earth and can provide valuable information concerning the sequence and timing of origination of derived characters. Knowledge of the timing of origination of synapomorphies makes it possible to estimate when unobserved character changes occurred in the geological past. Here we present a method for estimating the temporal interval during which synapomorphies evolved. The method requires either direct inclusion of fossil taxa (with or without extant taxa) in cladistic analyses based on morphological or combined data, or indirectly using the "molecular scaffold approach." Second, characters of interest are mapped on a most parsimonious tree and "minimum age node mapping" is used to place minimum ages on the nodes of the tree. Finally, characters of interest are evaluated for younger and/or older temporal constraints on the time of their origination; application of the older bound assumes ancestry of fossil terminals included in the tree. A key is provided herein describing the method. Among other applications, this approach has the potential to provide a powerful test of purported evolutionary cause-effect relationships. For example, the method has the ability to discover that derived characters of suggested adaptational significance may considerably pre-date the cause(s) that are hypothesized to have favored their establishment.

Crab scars reveal survival advantage of left-handed snails.

Biological asymmetries are important elements of the structure and function of many living organisms. Using the Plio-Pleistocene fossil record of crab predation on morphologically similar pairs of right- and left-handed snail species, we show here for the first time, contrary to traditional wisdom, that rare left-handed coiling promotes survival from attacks by right-handed crabs. This frequency-dependent result influences the balance of selection processes that maintain left-handedness at the species level and parallels some social interactions in human cultures, such as sports that involve dual contests between opponents of opposite handedness.