Shape disparity in the blade-like premolars of multituberculate mammals: functional constraints and the evolution of herbivory

Cimolodontan multituberculates were a diverse and long-lived group of mammals characterized by large, blade-like lower fourth premolars (p4). Blade-like (plagiaulacoid) dentitions have evolved numerous times in distantly related mammalian lineages. Here we investigate how p4-shape disparity changed through time in the Cimolodonta. We address two hypotheses: (H1) blade-like dentitions constrain the ability of plagiaulacoid mammals to evolve novel dental morphologies, (H2) cimolodontan dental evolution proceeded gradually along a morphocline during the Late Cretaceous. We quantify functionally important aspects of p4 shape, including ratios reflecting height (H:L), symmetry (L1:L), and mesial-face height (H1:H), in a large sample of cimolodontans spanning the mid-Cretaceous through early Paleogene of North America (ca. 100–35 Mya). Our results do not support the morphocline hypothesis (H2) and, instead, show that cimolodontans evolved a wide range of p4 shapes by the mid-Cretaceous, and that p4-shape disparity remained stable through the Late Cretaceous. We hypothesize that the two-stage cimolodontan chewing cycle (slicing-crushing then grinding) imposed functional constraints on p4 morphology. After the Cretaceous-Paleogene boundary, p4-shape disparity increased sharply, driven by the appearance of the Taeniolabidoidea, Microcosmodontidae, and Eucosmodontidae, in the early Paleocene. We contend that the slicing-crushing functions of the p4 became less important in those taxa, relaxing functional constraints on p4 morphology. Cimolodontans that retained both the slicing-crushing and grinding function of the p4 had a more limited range of p4 morphologies, and probably were largely restricted to animal-dominated omnivory. Taxa that shifted the initial slicing-crushing function from the p4 to the incisors had fewer functional constraints on p4 morphology, and were able to increase their molar grinding capacity to exploit plant-dominated omnivory and herbivory. That the p4 was reduced in herbivorous taxa rather than modified into a broader, multi-cusped tooth lends support to the morphological constraint hypothesis (H1), and this relationship between p4 morphology and function suggests that retaining a large, blade-like p4 might have limited the range of herbivorous diets cimolodontans could exploit. These findings highlight the ecological and evolutionary limitations that specialized dentitions can impose on mammals by restricting their morphological and, in turn, functional diversification.

Variations in the reproductive strategies of three populations of Phrynocephalus helioscopus in China

Background Egg size and clutch size are key life history traits. During the breeding period, it is possible for females to increase their reproductive output either by increasing the number of eggs if the optimal egg size (OES) is maintained, or by increasing the allocation of energy to each egg. However, the strategies adopted are often influenced by animals’ morphology and environment. Methods Here, we examined variation in female morphological and reproductive traits, tested for trade-offs between egg size and clutch size, and evaluated the relationship between egg size and female morphology in three populations of Phrynocephalus helioscopus. Results Female body size, egg size, and clutch size were larger in the Yi Ning (YN) and Fu Yun (FY) populations than in the Bei Tun (BT) population (the FY and YN populations laid more, and rounder eggs). Egg size was independent of female body size in two populations (BT and FY), even though both populations had an egg-size/clutch size trade-off. In the YN population, egg size and clutch size were independent, but egg size was correlated with female body size, consistent with the hypothesis of morphological constraint. Conclusions Our study found geographical variation in body size and reproductive strategies of P. helioscopus. Egg size was correlated with morphology in the larger-bodied females of the YN population, but not in the smaller-bodied females of the BT population, illustrating that constraints on female body size and egg size are not consistent between populations.

Idiomatic singleton or prototype? A productivity analysis of be-adj-and-v

This article addresses the morphological constraint on the ‘formulaic frame’ be-sure-and-v (Be sure and wear flowers in your hair!), whose idiomatic reading disappears in inflected uses (*She was sure and wore flower in her hair). This constraint also applies to certain verbal patterns (go/come-v, try-and-v) and is at least probabilistic for others (wait and see, go-and-v). A recent usagebased approach suggests that the so-called Bare Stem Condition follows from the semantics of the affected patterns, which are schematically non-assertive and thus functionally inappropriate for use in inflected, assertive environments. The same can be shown to apply to hortative be-sure-and-v, suggesting that the morphological behaviour of both verbal and adjectival pseudo-coordination have the same underlying functional-semantic constraint motivation. Supporting evidence comes from the status of be-sure-and-v relative to instantiations of the pattern: rather than being an idiosyncratic, isolated idiom, be-sure-and-v is a subtype of a moderately productive be-adj-and-v construction (be honest and admit, be patient and wait). Be-adj-and-v shows many of the characteristics of other pseudo-coordinated constructions, including the combination of semantically coherent slots fillers (flexible-adapt, glad-rejoice) and the asymmetric framing of single events. Methodologically, the article showcases how Collostructional Analyses can be used as diagnostic tools to identify (sub)types and slot-filler consistency in a bottom-up fashion, separating schema instantiations from syntagmatic ‘noise’ (i.e., the compositional adjectival predicate, My raspberries are ripe and taste delicious). Thus, the method identifies (and confirms) be-sure-and-v as the morphological, semantic, and statistical prototype of the more general schema.

Production and packaging of a biological arsenal: Evolution of centipede venoms under morphological constraint

Venom represents one of the most extreme manifestations of a chemical arms race. Venoms are complex biochemical arsenals, often containing hundreds to thousands of unique protein toxins. Despite their utility for prey capture, venoms are energetically expensive commodities, and consequently it is hypothesized that venom complexity is inversely related to the capacity of a venomous animal to physically subdue prey. Centipedes, one of the oldest yet least-studied venomous lineages, appear to defy this rule. Although scutigeromorph centipedes produce less complex venom than those secreted by scolopendrid centipedes, they appear to rely heavily on venom for prey capture. We show that the venom glands are large and well developed in both scutigerid and scolopendrid species, but that scutigerid forcipules lack the adaptations that allow scolopendrids to inflict physical damage on prey and predators. Moreover, we reveal that scolopendrid venom glands have evolved to accommodate a much larger number of secretory cells and, by using imaging mass spectrometry, we demonstrate that toxin production is heterogeneous across these secretory units. We propose that the differences in venom complexity between centipede orders are largely a result of morphological restrictions of the venom gland, and consequently there is a strong correlation between the morphological and biochemical complexity of this unique venom system. The current data add to the growing body of evidence that toxins are not expressed in a spatially homogenous manner within venom glands, and they suggest that the link between ecology and toxin evolution is more complex than previously thought.

The emergence of network structure, complementarity and convergence from basic ecological and genetic processes

Plant-animal mutualistic networks are highly diverse and structured. This has been explained by coevolution through niche based processes. However, this explanation is only warranted if neutral processes (e.g. limited dispersal, genetic and ecological drift) cannot explain these patterns. Here we present a spatially explicit model based on explicit genetics and quantitative traits to study the connection between genome evolution, speciation and plant-animal network demography. We consider simple processes for the speciation dynamics of plant-animal mutualisms: ecological (dispersal, demography) and genetic processes (mutation, recombination, drift) and morphological constraints (matching of quantitative trait) for species interactions, particularly mating. We find the evolution of trait convergence and complementarity and topological features observed in real plant-animal mutualistic webs (i.e. nestedness and centrality). Furthermore, the morphological constraint for plant reproduction generates higher centrality among plant individuals (and species) than in animals, consistent with observations. We argue that simple processes are able to reproduce some well known ecological and evolutionary patterns of plant-animal mutualistic webs.

Optimal egg size in a suboptimal environment: reproductive ecology of female Sonora mud turtles (Kinosternon sonoriense) in central Arizona, USA

We studied the reproductive ecology of female Sonora mud turtles (Kinosternon sonoriense) at Montezuma Well, a chemically-challenging natural wetland in central Arizona, USA. Females matured between 115.5 and 125 mm carapace length (CL) and 36-54% produced eggs each year. Eggs were detected in X-radiographs from 23 April-28 September (2007-2008) and the highest proportion (56%) of adult females with eggs occurred in June and July. Clutch frequency was rarely more than once per year. Clutch size was weakly correlated with body size, ranged from 1-8 (mean = 4.96) and did not differ significantly between years. X-ray egg width ranged from 17.8-21.7 mm (mean 19.4 mm) and varied more among clutches than within. Mean X-ray egg width of a clutch did not vary significantly with CL of females, although X-ray pelvic aperture width increased with CL. We observed no evidence of a morphological constraint on egg width. In addition, greater variation in clutch size, relative to egg width, suggests that egg size is optimized in this hydrologically stable but chemically-challenging habitat. We suggest that the diversity of architectures exhibited by the turtle pelvis, and their associated lack of correspondence to taxonomic or behavioral groupings, explains some of the variation observed in egg size of turtles.