An official website of the United States government
Abstract An ongoing challenge in macroevolutionary research is identifying common drivers of diversification amid the complex interplay of many potentially relevant traits, ecological contexts, and intrinsic characteristics of clades. In this study, we used geometric morphometric and phylogenetic comparative methods to evaluate the tempo and mode of morphological evolution in an adaptive radiation of Malagasy birds, the vangas, and their mainland relatives (Aves:Vangidae). The Malagasy radiation is more diverse in both skull and foot shape. However, rather than following the classic “early burst” of diversification, trait evolution accelerated well after their arrival in Madagascar, likely driven by the evolution of new modes of foraging and especially of a few species with highly divergent morphologies. Anatomical regions showed differing evolutionary patterns, and the presence of morphological outliers impacted the results of some analyses, particularly of trait integration and modularity. Our results demonstrate that the adaptive radiation of Malagasy vangas has evolved exceptional ecomorphological diversity along multiple, independent trait axes, mainly driven by a late expansion in niche space due to key innovations. Our findings highlight the evolution of extreme forms as an overlooked feature of adaptive radiation warranting further study.
more »
« less
Skull evolution and lineage diversification in endemic Malagasy carnivorans
Madagascar is one of the world’s foremost biodiversity hotspots with more than 90% of its species endemic to the island. Malagasy carnivorans are one of only four extant terrestrial mammalian clades endemic to Madagascar. Although there are only eight extant species, these carnivorans exhibit remarkable phenotypic and ecological diversity that is often hypothesized to have diversified through an adaptive radiation. Here, we investigated the evolution of skull diversity in Malagasy carnivorans and tested if they exhibited characteristics of convergence and an adaptive radiation. We found that their skull disparity exceeds that of any other feliform family, as their skulls vary widely and strikingly capture a large amount of the morphological variation found across all feliforms. We also found evidence of shared adaptive zones in cranial shape between euplerid subclades and felids, herpestids and viverrids. Lastly, contrary to predictions of adaptive radiation, we found that Malagasy carnivorans do not exhibit rapid lineage diversification and only marginally faster rates of mandibular shape evolution and to a lesser extent cranial shape evolution, compared to other feliforms. These results reveal that exceptional diversification rates are not necessary to generate the striking phenotypic diversity that evolved in carnivorans after their dispersal to and isolation on Madagascar.
more »
« less
- Award ID(s):
- 2128146
- PAR ID:
- 10613307
- Publisher / Repository:
- The Royal Society
- Date Published:
- Journal Name:
- Royal Society Open Science
- Volume:
- 11
- Issue:
- 10
- ISSN:
- 2054-5703
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Adaptive radiations are characterized by an increase in species and/or phenotypic diversity as organisms fill open ecological niches. Often, the putative adaptive radiation has been studied without explicit comparison to the patterns and rates of evolution of closely related clades, leaving open the question whether notable changes in evolutionary process indeed occurred at the origin of the group. Anolis lizards are an oft-used model for investigating the tempo and mode of adaptive radiations. Most of the prior research on the diversification of Anolis morphology has focused on the post-cranium because of its significance towards subdivision of the arboreal habitat. But the remarkable diversity in head shape in anoles has not been as thoroughly investigated. It remains unknown whether the tempo or mode of head shape diversification changed as anoles diversified. We performed geometric morphometric analysis of skull shape across a sample of 12 Iguanian families (110 species), including anoles. Anolis lizards occupy a unique area and a wider region of morphological space compared to the 11 other families examined. We did not find a difference in the evolutionary rate of head shape diversification between anoles and their relatives. Rather, the extraordinary amount of skull diversity arose through a distinct mode of evolution; anoles moved into novel regions by relatively large morphological transitions across morphological space compared to their relatives. Our results demonstrate that traits not directly tied to the adaptive shift of a lineage into unique ecological spaces may undergo exceptional patterns of change as the clade diversifies.more » « less
-
ABSTRACT Colonization of a novel habitat is often followed by radiation in the wake of ecological opportunity. Alternatively, some habitats should be inherently more constraining than others if the challenges of that environment have few evolutionary solutions. We examined the push-and-pull of these factors on evolution following habitat transitions, using anglerfishes (Lophiiformes) as a model. Deep-sea fishes are notoriously difficult to study, and poor sampling has limited progress thus far. Here we present a new phylogeny of anglerfishes with unprecedented taxonomic sampling (1,092 loci and 40% of species), combined with three-dimensional phenotypic data from museum specimens obtained with micro-CT scanning. We use these datasets to examine the tempo and mode of phenotypic and lineage diversification using phylogenetic comparative methods, comparing lineages in shallow and deep benthic versus bathypelagic habitats. Our results show that anglerfishes represent a surprising case where the bathypelagic lineage has greater taxonomic and phenotypic diversity than coastal benthic relatives. This defies expectations based on ecological principles since the bathypelagic zone is the most homogeneous habitat on Earth. Deep-sea anglerfishes experienced rapid lineage diversification concomitant with colonization of the bathypelagic zone from a continental slope ancestor. They display the highest body, skull and jaw shape disparity across lophiiforms. In contrast, reef-associated taxa show strong constraints on shape and low evolutionary rates, contradicting patterns suggested by other shallow marine fishes. We found that Lophiiformes as a whole evolved under an early burst model with subclades occupying distinct body shapes. We further discuss to what extent the bathypelagic clade is a secondary adaptive radiation, or if its diversity can be explained by non-adaptive processes.more » « less
-
Madagascar is famous today not only for its unique biodiversity, but also for the high levels of endemism of plants and animals. Less appreciated is the fact that, in the recent past, the island had even greater biodiversity with many other endemic animals such as giant lemurs, elephant birds, pygmy hippopotami, tortoises, and crocodiles that have gone extinct within the past 2000 years. The extinction of many of these groups is thought to be the result of both human activities and environmental change. Most research has focused on the lemurs, hippopotami, and elephant birds. Other recently extinct animals, including the Malagasy horned crocodile (Voay robustus), are relatively poorly known. Madagascar’s subfossil crocodylians include two taxa: the extinct V. robustus (the Malagasy horned crocodile) and the extant Crocodylus niloticus. The latter arrived on Madagascar relatively recently and we know little about the habitat preferences, distributions and ecological interactions (if any) of either species during the Holocene. In order to better understand the recent history of crocodylian extinction in Madagascar, we must first identify which species were present and where they were found. We present here a description of subfossil crocodylian material collected from the newly discovered subfossil site of Tsaramody (Sambaina Basin), a high-elevation wetlandenvironment. At 1655 m, it represents the highest elevation subfossil site on the island. Here we describe both cranial (e.g., premaxillary, jugal, and squamosal “horns”) and postcranial elements (e.g., osteoderms). Our research indicates that crocodile material from Tsaramody appears morphologically to belong to V. robustus, the extinct species. However, oval tuberosities on the frontal bone and a triangular extension of the squamosal bone suggest previously unrecognized variation.more » « less
-
Synopsis The concept of modularity is fundamental to understanding the evolvability of morphological structures and is considered a central framework for the exploration of functionally and developmentally related subsets of anatomical traits. In this study, we explored evolutionary patterns of modularity and integration in the 4-bar linkage biomechanical system of the skull in the fish family Labridae (wrasses and parrotfishes). We measured evolutionary modularity and rates of shape diversification of the skull partitions of three biomechanical 4-bar linkage systems using 205 species of wrasses (family: Labridae) and a three-dimensional geometric morphometrics data set of 200 coordinates. We found support for a two-module hypothesis on the family level that identifies the bones associated with the three linkages as being a module independent from a module formed by the remainder of the skull (neurocranium, nasals, premaxilla, and pharyngeal jaws). We tested the patterns of skull modularity for four tribes in wrasses: hypsigenyines, julidines, cheilines, and scarines. The hypsigenyine and julidine groups showed the same two-module hypothesis for Labridae, whereas cheilines supported a four-module hypothesis with the three linkages as independent modules relative to the remainder of the skull. Scarines showed increased modularization of skull elements, where each bone is its own module. Diversification rates of modules show that linkage modules have evolved at a faster net rate of shape change than the remainder of the skull, with cheilines and scarines exhibiting the highest rate of evolutionary shape change. We developed a metric of linkage planarity and found the oral jaw linkage system to exhibit high planarity, while the rest position of the hyoid linkage system exhibited increased three dimensionality. This study shows a strong link between phenotypic evolution and biomechanical systems, with modularity influencing rates of shape change in the evolution of the wrasse skull.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1098/rsos.240538
