Evolutionary Patterns in Advanced Snakes

One prevalent view of phylogenetic events in advanced snakesholds that the fangs evolved along at least two pathways one(e.g. elapids) from ancestors with enlarged anterior and theother (e.g. viperids) from ancestors with enlarged posteriormaxillary teeth. Selective forces driving these changes arepresumed to arise from the increasing advantages of teeth andglands in venom injection. In this paper another plausible viewof these events is proposed. First fangs of both elapids and viperids likely evolved fromreal maxillary teeth. In non-venomous snakes, differences intooth morphology and function suggest that there may be somedivision of labor among anterior and posterior maxillary teeth.Anterior maxillary teeth, residing forward in the mouth likelyserve the biological role of snaring and impaling prey duringthe strike. They are also conical frequently recurved and lacka secretion groove. On the other hand posterior teeth becauseof their geometric position on the maxilla and mechanical advantages,tend to serve as aids in preingestion manipulation and swallowingof prey. They are often blade shaped and occasionally bear asecretion groove along their sides. Although both front andrear maxillary teeth of nonvenomous snakes may be elongatedthis is likely to serve these different functional roles andhence they evolved under different selective pressures. Whenfangs evolved they did so several times independently but fromrear maxillary teeth. In support one notes a) the similar positionpostorbital of venom and Duvernoy s glands b) similar embryonicdevelopment of fangs and rear maxillary teeth c) secretion groovewhen present, is found only on rear teeth and d) similar biologicalroles of some rear teeth and fangs. For ease in clearance ofthe prey during the strike the fangs are positioned forwardin the mouth accomplished in viperid snakes by forward rotationof the maxilla and elapids by rostral anatomical migration tothe front of the maxilla. Second, the adaptive advantage first favoring initial rear toothenlargement likely centered not on their role in venom injectionbut rather on their role in preingestion manipulation and swallowing.However once enlarged, teeth would be preadapted for later modificationinto fangs under selection pressures arising from advantagesof venom introduction. This has implications for the function and evolution of associatedstructures. Besides possibly subduring or even killing of preythe secretion of Duvernoy's gland may be involved in digestionor in neutralizing noxious or fouling products of the prey.The presence or absence of constriction need not be functionallytied to absence or presence of venom injection. The phylogeneticpathways outlined herein were likely traveled several timesindependently in advanced snakes.     

Evolution of venom delivery structures in madtom catfishes (Siluriformes: Ictaluridae)

The use of venom to subdue prey or deter predators has evolved multiple times in numerous animal lineages. Catfishes represent one of the most easily recognized, but least studied groups of venomous fishes. Venom glands surround spines on the dorsal and pectoral fins that serve as venom delivery structures. Species of madtom catfishes in the genus Noturus were found to each have one of four venom delivery morphologies: (1) smooth spine with no venom gland; (2) smooth spine with venom gland associated with shaft of spine; (3) serrated spine with venom gland associated with shaft of spine; and (4) serrated spine with venom gland associated with shaft of spine and posterior serrations. Analyses accounting for the phylogenetic history of Noturus species suggest that a serrated pectoral spine with a venom gland is the ancestral condition for the genus. The presence of serrations and a venom gland have been largely conserved among Noturus species, but sting morphology has changed at least five times within the genus. Four of these changes have resulted in a loss of morphological complexity, including the loss of posterior serrations, loss of venom glands associated with the posterior serrations, and one complete loss of the venom gland. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 115–129.     

Adaptive modifications of carapace outlines in the Cytheroidea (Ostracoda: Crustacea)

Shell outlines of 202 extant cytheroidean ostracods were analysed in dorsal, lateral, and posterior views by elliptic Fourier analysis. The results obtained confirm that the exterior morphology is related to ecological factors as well as phylogenetic constraints. Phytal species living on tall seagrass and benthic species burrowing in sediments are characterized and differentiated from the species crawling on sediments by the presence of slender shells with tapered venters. With reference to reconstruction of ancestral state of outline traits on the molecular phylogeny, the hypothetical ancestor of cytheroidean ostracods is presumed to have had an average-shaped shell. Morphological plasticity of the shell outline was observed in many families. The phytal species living on tall seagrass appear to have evolved convergently with species from other habitats, acquiring slim shell outlines during the Cenozoic period. The present analysis also reveals the phylogenetic constraints on the morphological evolution of the Trachyleberididae in their adaptation to a burrowing habit.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 810–821.     

Activity of Head Muscles During Feeding by Snakes: A Comparative Study

The adaptive radiation of colubroid snakes has involved thedevelopment of numerous prey capture specializations combinedwith conservation of a swallowing mechanism characterized byindependent movements of the right and left toothed bones ofthe skull. Synchronized electromyographic and cinematographicrecordings of swallowing in Nerodia, Elaphe, Heterodon and Agkistrodon,four diverse genera of colubroid snakes, allow a preliminaryevaluation of the relationship between prey capture and swallowing.The results indicate that the movements of the palatopterygoidbar and advance of the mandible as closing of the jaws beginsas well as patterns of muscle activity producing these movementsare similar among the four genera. Conversely, the patternsof activity of external adductors and, to some extent, the depressormandibulae differ among the four genera sampled. Analyses ofbone movements during swallowing suggest that swallowing iseffected primarily by the palatopterygoid bars. The mandiblesand their connecting soft tissues mainly press the prey againstthe palatopterygoid teeth. The mandibular teeth evidently playlittle active role in swallowing. Also, the maxilla, which displaysconsiderable morphological diversity among colubroid snakes,has little independent or direct function in swallowing, itsteeth rarely contacting the prey. The data suggest that theheads of colubroid snakes have evolved two partially separatedstructural-functional units, a medial swallowing unit and alateral prey capture unit.     

The origin of snakes (Serpentes) as seen through eye anatomy

Snakes evolved from lizards but have dramatically different eyes. These differences are cited widely as compelling evidence that snakes had fossorial and nocturnal ancestors. Their eyes, however, also exhibit similarities to those of aquatic vertebrates. We used a comparative analysis of ophthalmic data among vertebrate taxa to evaluate alternative hypotheses concerning the ecological origin of the distinctive features of the eyes of snakes. In parsimony and phenetic analyses, eye and orbital characters retrieved groupings more consistent with ecological adaptation rather than accepted phylogenetic relationships. Fossorial lizards and mammals cluster together, whereas snakes are widely separated from these taxa and instead cluster with primitively aquatic vertebrates. This indicates that the eyes of snakes most closely resemble those of aquatic vertebrates, and suggests that the early evolution of snakes occurred in aquatic environments.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81 , 469–482.     

后毒牙类毒蛇

长期以来,人们仅把具有沟牙和管牙的蛇视为毒蛇,然而,近年来发现游蛇科中的虎斑颈槽蛇、红脖颈槽蛇、颈棱蛇、赤链蛇等既无管牙,也无沟牙,却频频发生这类蛇咬伤人后引起中毒的事例,甚至出现被咬伤致严重出血休克死亡的事件。经深入研究后发现,这些蛇虽没有沟牙和管牙,但却具有产生毒性分泌物的毒腺—杜氏腺(Duvernoy′s gland)及皮下腺,且不同的毒腺具有不同的毒性作用,可表现为出血不止、溶血、呼吸困难、肾损害等。这类蛇与毒腺的导管有联系的上颌牙明显粗大,上颌牙与上颌骨、横骨连接牢固,毒腺里的毒液可顺着粗大的上颌牙流入伤口,因此,应视为"后毒牙类毒蛇"。     

Evidence for speciational change in the evolution of ratites (Aves: Palaeognathae)

To perform a comparative analysis of character associations framed in a phylogenetic context (e.g. independent contrasts), a model of character evolution must be assumed. According to phyletic gradualism, morphological change accumulates gradually over time within lineages, and speciation events do not have a major role. Under speciational models, morphological change is assumed to occur during or just after cladogenesis in both daughter species, and the resulting morphologies do not change over long periods of time (stasis), until the next cladogenetic event. A novel method is presented for comparing these models of character evolution that uses permutational multiple phylogenetic regressions. The addition of divergence times to well-corroborated phylogenetic trees and the utilization of the method developed in this paper allows the estimation of relative frequency of gradual change and speciational change from living organisms. This method is applied to a dataset from ratites with the conclusion that, for a range of morphological features, change tends to have been speciational rather than gradual.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 99–106.     

Dangerous food: lacking venom and constriction,how do snake‐like lizards (Lialis burtonis,Pygopodidae) subdue their lizard prey?

Snakes are renowned for their ability to subdue and swallow large, often dangerous prey animals. Numerous adaptations, including constriction, venom, and a strike-and-release feeding strategy, help them avoid injury during predatory encounters. Burton's legless lizard ( Lialis burtonis Gray, Pygopodidae) has converged strongly on snakes. It is functionally limbless and feeds at infrequent intervals on relatively large prey items (other lizards) capable of inflicting a damaging bite. However, L. burtonis possesses neither venom glands, nor the ability to constrict prey. We investigated how L. burtonis subdues its prey without suffering serious retaliatory bites. Experiments showed that lizards modified their strike precision according to prey size; very large prey were always struck on the head or neck, preventing them from biting. In addition, L. burtonis delayed swallowing large lizards until they were incapacitated, whereas smaller prey were usually swallowed while still struggling. Lialis burtonis also displays morphological adaptations protecting it from prey retaliation. Its long snout prevents prey from biting, and it can retract its lidless eyes out of harm's way while holding onto a food item. The present study further clarifies the remarkable convergence between snakes and L. burtonis , and highlights the importance of prey retaliatory potential in predator evolution.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91 , 719–727.     

Morphological correlates of ant eating in horned lizards (Phrynosoma)

The North American horned lizards ( Phrynosoma ) represent a morphologically specialized group of ant-eating lizards. Although variation in dietary fidelity is observed among the species, all appear to possess morphological specializations thought to be related to their ant-eating diets. Previous studies have examined morphological specialization in Phrynosoma , but they have not taken into account the phylogenetic relationships of its member species. In the present study, the morphological characteristics of the head, jaws and teeth that are thought to be important in prey capture and prey processing were examined to test whether variation in cranial morphology is associated with diet in lizards of the genus Phrynosoma . It is suggested that lizards of the genus Phrynosoma are indeed morphologically specialized and that ant-eating is associated with reduced dentition and an overall reduction in the robustness of morphological structures important in prey processing. Although this trend holds for the highly myrmecophagous species of Phrynosoma , a robust cranial morphology is apparent in the short-horned lizard clade ( Phrynosoma ditmarsi , Phrynosoma douglasii , Phrynosoma hernandesi , Phrynosoma orbiculare ), implying the ability to process a variety of dietary items. The present study suggests that additional feeding specializations exist within an already specialized clade (i.e. the short-horned lizard clade) and highlights the need for more detailed dietary and behavioural studies of feeding behaviour in this uniquely specialized group of lizards.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 13–24.     

Molecular systematics of North American phoxinin genera (Actinopterygii: Cyprinidae) inferred from mitochondrial 12S and 16S ribosomal RNA sequences

The cyprinid fish fauna of North America is relatively large, with approximately 300 species, and all but one of these are considered phoxinins. The phylogenetic relationships of the North American phoxinins continue to pose difficulties for systematists. Results of morphological analyses are not consistent owing to differences interpreting and coding characters. Herein, we present phylogenetic analyses of mitochondrial 12S and 16S ribosomal RNA sequence data for representatives of nearly all genera of North American phoxinins. The data were analysed using parsimony, weighted parsimony, maximum likelihood and bayesian analyses. Results from weighted parsimony, likelihood and the bayesian analysis are largely consistent as they all account for differing substitution rates between transitions and transversions. Several major clades within the fauna can be recognized and are strongly supported by all analyses. These include the western clade, creek chub–plagopterin clade and the open posterior myodome clade. The shiner clade is nested in the open posterior myodome clade and is the most species-rich clade of North American phoxinins. Relationships within this clade were not well resolved by our analyses. This may reflect the inability of the mitochondrial RNA genes to resolve recent speciation events or taxon sampling within the shiner clade.  © 2003 The Linnean Society of London, Zoological Journal of the Linnean Society , 2003, 139 , 63–80.     

A phylogenetic analysis of the genera of Lejeuneaceae (Hepaticae)

The Lejeuneaceae are the largest family of the liverworts (Hepaticae), with almost a thousand species in 91 currently accepted genera. We analysed phylogenetic relationships of 69 genera, representing all major subfamilies and tribes recognized in the family, by using 49 informative morphological characters (31 gametophytic, 18 sporophytic), one chemical character, and applying equal and successive weighting of characters and parsimony analysis. In all trees recovered, the Lejeuneaceae were monophyletic with Nipponolejeunea (subfam. Nipponolejeuneoideae) forming the basalmost lineage. The remaining genera clustered in two major groups, the monophyletic Lejeuneoideae (52 genera) and the paraphyletic Ptychanthoideae (16 genera). Within each, several multigeneric lineages corresponding in part to previously described taxa were recovered: the Acrolejeuneinae and Ptychanthinae clades in the Ptychanthoideae, and the Brachiolejeuneinae, Lejeuneeae and Tuyamaella–Cololejeunea clades in the Lejeuneoideae. Bryopteris , a genus sometimes treated as a separate family, was nested in the Ptychanthinae clade. The Tuyamaella–Cololejeunea lineage corresponded with three previously recognized subfamilies (Cololejeuneoideae, Myriocoleoideae and Tuyamaelloideae) and contained genera with neotenic features, in two subclades. These features seemed to have originated by multiple heterochronic events: single origins were detected for 'protonemal neoteny' and 'primary neoteny', whereas 'secondary neoteny' probably evolved twice. Relationships within the large Lejeuneeae clade (43 genera) remained largely unresolved, although several putative lineages were detected in majority rule trees. Additional characters such as DNA sequences may provide better phylogenetic resolution in this group.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 391–410.     

A new phylogenetic classification for the gymnophthalmid genera Cercosaura , Pantodactylus and Prionodactylus (Reptilia: Squamata)

Because of the poor state of knowledge of many of the gymnophthalmid genera, systematic revision is necessary to render the classification consistent with evolutionary history. To that end, I conducted a review of the species of three genera of the Cercosaurinae which appear to form a monophyletic group: Cercosaura , Pantodactylus , and Prionodactylus . Phylogenetic analysis of 61 morphological characters was conducted after specimens of all species were examined to evaluate the composition of each taxon. The phylogenetic reconstruction suggested that the genus Prionodactylus was paraphyletic. A new phylogenetic classification is proposed that synonymizes Pantodactylus and Prionodactylus with Cercosaura. Cercosaura is redefined to include 11 species and seven subspecies. A key is provided to distinguish among species.  © 2003 The Linnean Society of London, Zoological Journal of the Linnean Society, 2003, 137 , 101−115.     

Phylogeny of Courtship and Male-Male Combat Behavior in Snakes

Background

Behaviors involved in courtship and male-male combat have been recorded in a taxonomically broad sample (76 species in five families) of snakes in the clade Boidae + Colubroidea, but before now no one has attempted to find phylogenetic patterns in such behaviors. Here, we present a study of phylogenetic patterns in such behaviors in snakes.

Methodology/Principal Findings

From the literature on courtship and male-male combat in snakes we chose 33 behaviors to analyze. We plotted the 33 behaviors onto a phylogenetic tree to determine whether phylogenetic patterns were discernible. We found that phylogenetic patterns are discernible for some behaviors but not for others. For behaviors with discernible phylogenetic patterns, we used the fossil record to determine minimum ages for the addition of each behavior to the courtship and combat behavioral repertoire of each snake clade.

Conclusions/Significance

The phylogenetic patterns of behavior reveal that male-male combat in the Late Cretaceous common ancestors of Boidae and Colubridae involved combatants raising the head and neck and attempting to topple each other. Poking with spurs was added in Boidae. In Lampropeltini the toppling behavior was replaced by coiling without neck-raising, and body-bridging was added. Phylogenetic patterns reveal that courtship ancestrally involved rubbing with spurs in Boidae. In Colubroidea, courtship ancestrally involved chin-rubbing and head- or body-jerking. Various colubroid clades subsequently added other behaviors, e.g. moving undulations in Natricinae and Lampropeltini, coital neck biting in the Eurasian ratsnake clade, and tail quivering in Pantherophis. The appearance of each group in the fossil record provides a minimum age of the addition of each behavior to combat and courtship repertoires. Although many gaps in the story of the evolution of courtship and combat in snakes remain, this study is an important first step in the reconstruction of the evolution of these behaviors in snakes.     

Convergent body flattening in a clade of tropical rock-using lizards (Scincidae: Lygosominae)

The repeated occurrence of similar morphologies in organisms from similar habitats provides good evidence of convergent selection, and convergent patterns of evolutionary change. In lizards, a flattened morphology has often been noted; however, whether this trait is convergent in specific habitats has never been tested using phylogenetic methods. The present study examined patterns of morphological convergence in 18 species of tropical Lygosomine skinks from three broad habitat categories (generalist, leaf litter-dwelling, and rock-using species). In general, although there where relatively few morphological differences of species from different habitats, phylogenetic analyses revealed that rock-using species have consistently and repeatedly evolved a dorsoventrally flattened head and body. The adaptive basis of this flattened morphology is consistent with both biomechanical predictions of performance (e.g. climbing locomotion) and ecology (e.g. use of rock crevices, camouflage) of species that occupy rocky habitats.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 399–411.     

Morphology and function of the head in foetal and juvenile Scolecomorphus kirkii (Amphibia: Gymnophiona: Scolecomorphidae)

The external and musculoskeletal morphology of the head is described for an ontogenetic series of the scolecomorphid caecilian Scolecomorphus kirkii . The rostral region of foetuses and juveniles is expanded into large, posterolaterally pointing paraoral processes that are formed by the maxilla. Extraoral teeth are present on the underside of the rostrum and laterally on the paraoral processes. In the foetuses, teeth are covered by epidermal tissue. The endoskeletal part of the foetal skull is largely cartilaginous, but all of the dermal bones, with the exception of the squamosal, are present. The foetal chondrocranium is extensively developed and shows a peculiar, posterolateral process of the nasal capsule that is connected to the trabecula cranii by a transverse bar posterior to the choana, and extends further posterior beyond the level of the posterior end of the pila antotica. Only two mm. adductor mandibulae are present, together with two pterygoideus muscles that insert onto the lower jaw. The palatoquadrate and quadrate of foetuses and juveniles, respectively, are highly mobile. It is suggested that the derived head morphology of Scolecomorphus foetuses and juveniles is an adaptation to specialized postparitive feeding.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 491–504.     

Morphological and ecological convergence in two natricine snakes

Similar morphologies between species may be due to shared ancestry or convergent evolution . Understanding instances of morphological and ecological convergence is central to evolutionary ecology because they help us understand the fit between organism and environment. Two species of stream-dwelling natricine snakes, Thamnophis rufipunctatus and Nerodia harteri present a model system for studying ecological and morphological convergence and adaptation. The species are allopatric and both live in shallow riffles in streams and forage visually for fish. We studied morphological similarity, trait evolution and functional significance of ecologically relevant traits in these and related species, and used mitochondrial DNA sequences for the ND4 gene to estimate their phylogenetic relationships. Character mapping of head length and head width supported the hypothesis of independent evolution of head shape in T .  rufipunctatus and N .  harteri . The elongate snout is a derived trait in these two taxa that is associated with reduced hydrodynamic drag on the snakes' heads when in a swift current, compared to other species with the ancestral blunt snout. We hypothesize that lower hydrodynamic drag facilitates prey capture success in these species that are known to forage by holding their position in currents and striking at fish prey. The elongate snout morphology has also resulted in a diminished binocular vision field in these snakes, contrary to the hypothesis that visually orientated snakes should exhibit relatively greater binocular vision. Convergent evolution of the long snout and reduced hydrodynamic drag in T. rufipunctatus and N. harteri are consistent with the hypothesis that the long snout is an adaptation to foraging in a swift current.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 363–371.     

Phylogenetics of advanced snakes (Caenophidia) based on four mitochondrial genes

Phylogenetic relationships among advanced snakes (Acrochordus + Colubroidea = Caenophidia) and the position of the genus Acrochordus relative to colubroid taxa are contentious. These concerns were investigated by phylogenetic analysis of fragments from four mitochondrial genes representing 62 caenophidian genera and 5 noncaenophidian taxa. Four methods of phylogeny reconstruction were applied: matrix representation with parsimony (MRP) supertree consensus, maximum parsimony, maximum likelihood, and Bayesian analysis. Because of incomplete sampling, extensive missing data were inherent in this study. Analyses of individual genes retrieved roughly the same clades, but branching order varied greatly between gene trees, and nodal support was poor. Trees generated from combined data sets using maximum parsimony, maximum likelihood, and Bayesian analysis had medium to low nodal support but were largely congruent with each other and with MRP supertrees. Conclusions about caenophidian relationships were based on these combined analyses. The Xenoderminae, Viperidae, Pareatinae, Psammophiinae, Pseudoxyrophiinae, Homalopsinae, Natricinae, Xenodontinae, and Colubrinae (redefined) emerged as monophyletic, whereas Lamprophiinae, Atractaspididae, and Elapidae were not in one or more topologies. A clade comprising Acrochordus and Xenoderminae branched closest to the root, and when Acrochordus was assessed in relation to a colubroid subsample and all five noncaenophidians, it remained associated with the Colubroidea. Thus, Acrochordus + Xenoderminae appears to be the sister group to the Colubroidea, and Xenoderminae should be excluded from Colubroidea. Within Colubroidea, Viperidae was the most basal clade. Other relationships appearing in all final topologies were (1) a clade comprising Psammophiinae, Lamprophiinae, Atractaspididae, Pseudoxyrophiinae, and Elapidae, within which the latter four taxa formed a subclade, and (2) a clade comprising Colubrinae, Natricinae, and Xenodontinae, within which the latter two taxa formed a subclade. Pareatinae and Homalopsinae were the most unstable clades.