The giraffe (Giraffa camelopardalis) cervical vertebral column: a heuristic example in understanding evolutionary processes?

The current study considers the osteological morphology of the giraffe (Giraffa camelopardalis) vertebral column, with emphasis on evaluating both the adaptive and constraining features compared with other ungulates as a heuristic example in understanding evolutionary processes. Vertebral columns of giraffes varying in age from calf to adult were studied in order to understand the potential evolutionary scenarios that might have led to the modern phenotype. Data from the giraffe sample were then compared with the results from several other ungulate species, including the okapi and two species of camelids that also have visibly elongated necks. Our results show that the elongated neck of the modern giraffe appears to specifically result from evolutionary changes affecting the seven cervical vertebrae, independent of the remainder of the vertebral column. The cervical vertebrae comprise over half of the length of the total vertebral column in the giraffe. The increases in cervical vertebrae lengths also appear to be allometrically constrained, with alterations in the overall length of the neck resulting from the elongation of the entire cervical series, rather than from a single vertebra or subset of vertebrae. We place our results in the context of hypotheses concerning the origin and evolution of the giraffe neck, and the evolution of long necks in a broader sense. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 736–757.     

Seed morphology and anatomy of Austrotaxus spicata (Taxaceae) and its systematic position

The anatomy and ultrastructure of seed envelopes of a New Caledonian endemic Austrotaxus spicata were examined for the first time. The systematic position and phylogenetic relations of Austrotaxus were analysed in light of these data. The structure of aril and spermoderm were investigated to demonstrate the similarities with Phyllocladus as well as with Taxus and Pseudotaxus . On the basis of all female reproductive organ characters, Austrotaxus appeared to be fairly isolated and its placing in the independent family Austrotaxaceae was confirmed from the standpoint of comparative anatomy of the seed coat. Taking into consideration that the heterobathmy of features can be the most distinctively traced in the structure of reproductive organs, evaluating the extent of evolutionary advancement of Austrotaxus seems to be rather difficult. However, it is evident that the relationship of Austrotaxus either with Taxaceae or with Podocarpaceae s.l . is considerably remote.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 437–443.     

Evolution of axial patterning in elongate fishes

Within the ray-finned fishes, eel-like (extremely elongate) body forms have evolved multiple times from deeper-bodied forms. Previous studies have shown that elongation of the vertebral column may be associated with an increase in the number of vertebrae, an increase in the length of the vertebral centra, or a combination of both. Because the vertebral column of fishes has at least two anatomically distinct regions (i.e. abdominal and caudal), an increase in the number and relative length of the vertebrae could be region-specific or occur globally across the length of the vertebral column. In the present study, we recorded vertebral counts and measurements of vertebral aspect ratio (vertebral length/width) from museum specimens for 54 species representing seven groups of actinopterygian fishes. We also collected, from published literature, vertebral counts for 813 species from 14 orders of actinopterygian and elasmobranch fishes. We found that the number of vertebrae can increase independently in the abdominal and caudal regions of the vertebral column, but changes in aspect ratio occur similarly in both regions. These findings suggest that abdominal vertebral number, caudal vertebral number, and vertebral aspect ratio are controlled by separate developmental modules. Based on these findings, we suggest some candidate developmental mechanisms that may contribute to vertebral column patterning in fishes. Our study is an example of how comparative anatomical studies of adults can generate testable hypotheses of evolutionary changes in developmental mechanisms.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 97–116.     

Incipient speciation driven by phenotypic plasticity? Evidence from sympatric populations of Arctic charr

Recent models suggest that the existence of environmentally induced polymorphisms within a single population (especially those related to foraging) facilitates the process of evolutionary divergence within a single gene pool by generating distinct phenotypic modes that are exposed to differential selection. In order to test a prediction of the phenotypic plasticity model of divergence, we used a well-documented polymorphism to disentangle the relative effects of morph and rearing environment in generating phenotypic variance. We reared first-generation offspring of two sympatric morphs of Arctic charr Salvelinus alpinus in the laboratory and compared their head morphology with that of their wild parents. Morphological characters with a known functional role in foraging were highly plastic. Rearing environment accounted for the largest component of the variation in expressed phenotype, but this environmental effect overlaid a clear (but small) genetic effect. We conclude that phenotypic plasticity has played a significant role in the evolution of this trophic polymorphism, but that the evolutionary process has progressed to the point that the gene pool is now segregated.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 611–618.     

Latitudinal variation in axial patterning of the medaka (Actinopterygii: Adrianichthyidae): Jordan's rule is substantiated by genetic variation in abdominal vertebral number

Because the body axes of fish consist of two anatomically distinct vertebrae, abdominal and caudal, one type may be more variable in number than the other and thus contribute more to morphological diversification. Jordan's rule, a geographical tendency for fish from higher latitudes to have more vertebrae, has not been examined in terms of numbers of abdominal and/or caudal vertebrae, despite its prevalence. Vertebral observations of wild populations of the medaka ( Oryzias latipes ) revealed that the latitudinal increase in vertebral number is caused by an increase in abdominal vertebrae; caudal vertebrae did not vary systematically across latitudes. Laboratory experiments revealed that this latitudinal cline in abdominal vertebral number persists in a range of common environments, demonstrating a genetic basis. Phenotypic plasticity was also evident: lower developmental temperatures resulted in more abdominal vertebrae. This indicates that greater numbers of abdominal vertebrae in higher latitude individuals in the wild may be caused not only by genetic factors but by lower habitat temperatures, although the contribution of the former to Jordan's rule is assessed to be much greater. The genetic basis of the latitudinal variation in abdominal vertebral number suggests that selection on functions associated with abdominal regions is the probable explanation for Jordan's rule in this fish.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 856–866.     

Functional differentiation of African grazing ruminants: an example of specialized adaptations to very small changes in diet

We assess whether interspecific differences in craniodental morphology within a single ruminant feeding guild, the grazers, represent anatomical adaptations to subtle differences in diet. Differences in craniodental anatomy follow a distinct taxonomic pattern that is paralleled by dietary niche differentiation recorded in species' stable carbon (δ¹³C) and nitrogen isotope (δ¹⁵N) compositions, strongly supporting a hypothesis for functional divergence within the grazers. We propose that the evolutionary origin of grazers were multifold; at least two and up to four different types of grazing can be discerned within the 11 taxa studied here alone. However, correspondence between craniodental adaptations and isotopic differences across species are not found when only δ¹³C data are considered (i.e. morphological differences do not reflect varying proportions of C₃ browse to C₄ grass consumed). This implies that alternate anatomical adaptations to grazing are not related to differences between variable (part-time browsing) and obligate grazers, as previously predicted. Rather, anatomical differences correlate strongly with changes in δ¹⁵N, which we infer to reflect functional responses to changes in diet quality associated with the degree of feeding selectivity and short-, medium-, or tall-grass grazing.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 755–764.     

Intraspecific variation in the postcranial skeleton morphology in African clariids: a case study of extreme phenotypic plasticity

Taxonomic relationships within the Clariidae, especially within the anguilliform species, are currently ambiguous due to the lack of a reliable structure of valid generic and specific characteristics. Based on the information available, it is difficult to properly diagnose the different elongated genera and species; this is due in part to a high degree of variability of certain traits generally considered to be important taxonomically. For example, the caudal skeleton is often considered to be an important diagnostic trait. However, the degree of phenotypic plasticity has not hitherto been adequately assessed. This paper deals with interspecific variation of the caudal skeleton of Clarias gariepinus , Platyallabes tihoni , Platyclarias machadoi , Gymnallabes typus , Channallabes apus and Dolichallabes microphthalmus . The caudal skeleton of C. apus is studied, using specimens from three regions in Gabon. Hypural fusions and haemal and neural spines show most variation. The observed morphological variation appears to be geographically independent, in contrast to other morphological features such as vertebrae.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 437–446.     

Convergent evolution of shell shape in freshwater limpets: the African genus Burnupia

Convergent evolution of shell shape is a well known phenomenon in gastropods that has caused much confusion in taxonomic and systematic studies. A paradigm is the patelliform shell shape in several taxa of the order Basommatophora. Historically, most freshwater limpets were assigned to the family Ancylidae. Based on anatomical data, some taxa were subsequently moved to different families. However, there are still doubts about the monophyly of the remaining ancylids. This is also true for the African limpets and particularly for species of the genus Burnupia Walker, 1912. In the present paper, two independent molecular markers (COI, 18S rRNA) are used to (a) infer the position of Burnupia within the Basommatophora and (b) to test whether the shell shape of Burnupia evolved independently. Bayesian and maximum likelihood analyses of 12 genera of limnic Basommatophora indicate that Burnupia not only appears to be distinct from the Ancylidae, but also from all other representatives of the superfamily Planorboidea studied here. Based on a generally well-supported phylogeny and preliminary anatomical data, it is concluded that patelliform shell shapes evolved at least three times in the taxa studied here and that the shell shape of Burnupia represents another case of convergent evolution. Previously proposed functional and evolutionary scenarios for the evolution of patelliform shell and their relevance for freshwater limpets are discussed.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 577–586.     

Evolution of South American mammalian predators (Borhyaenoidea): anatomical and palaeobiological implications

The evolution of South American carnivorous marsupials, the borhyaenoids, has been investigated through the functional analysis of postcranial adaptive traits and palaeobiological data. There is evidence that the evolutionary history of Borhyaenoidea proceeded from a noncursorial ancestor. The locomotion and habits of the early Palaeocene Mayulestes ferox probably approached a generalized plesiomorphic pattern for marsupial locomotion, i.e. primarily terrestrial with secondary arboreal adaptations. An exceptionally rich early Miocene Patagonian fauna has yielded various morphological predator types, from scansorial ambusher to terrestrial, incipiently cursorial, taxa. The most specialized borhyaenoid was the powerful sabretooth Thylacosmilus atrox that survived until the late Pliocene. The evolution from a scansorial pattern towards a cursorial trend, illustrated by Borhyaena tuberata , and towards the probable development of postlactational parental care in Thylacosmilus , required by its dental specialization and killing strategy, suggests a modification of the selective pressures and predatory activities of the group over evolutionary time.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 487–521.     

Hypocotyl features of Myrtus communis (Myrtaceae): a many-sided strategy for possible enhancement of seedling establishment in the Mediterranean environment

Seed germination and seedling development were studied in Myrtus communis L. (Myrtaceae), an evergreen shrub widespread in Mediterranean woodlands, maquis and garrigues, to investigate the presence of morphological and anatomical adaptations that enhance successful seedling establishment under biotic and abiotic stresses. Seeds were germinated under controlled conditions and were observed daily to identify different post-germination stages of development. The anatomy of developing hypocotyls and emerging radicles was studied through light and epi-fluorescence microscopy using both cross and longitudinal sections. Tegument rupture was caused by hypocotyl elongation, which, when water availability in the substrate was limited, was accompanied by a dense ring of hairs in the lower region. Absorption tests showed that the hypocotyl hairs were functional in water uptake. They might also enhance the anchorage of the seedling to the substrate. Further investigations showed the early formation of a suberized layer of cells (exodermis) in the radicle and the occurrence of phenolics in the hypocotyl cells of cortical parenchyma. In conclusion, our results show that seedlings of M. communis have developed a strategy of establishment that: (a) regulates water uptake through hypocotyl hairs and the exodermis; (b) might allow mechanical support through hypocotyl hairs; and (c) accumulates phenolics that might defend the plant against animal predation.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 195–202.     

Exploring the genomic mysteries of polyploidy in cotton

For several years allopolyploid cottons have been the subject of evolutionary investigations into the genomic mysteries of polyploidy. An array of genomic interactions have been documented, including interlocus concerted evolution, differential rates of genomic evolution and intergenomic sequence transfer. Substantial alterations in gene expression have occurred in response to allopolyploidization, including gene silencing and expression changes that vary by organ. Some of the molecular phenomena occurring in polyploids appear to be non-Mendelian. Many of the genomic and expression alterations have occurred on an evolutionary timescale, whereas others reflect more immediate consequences of genomic merger.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82 , 573–581.     

Functional anatomy and biomechanics of the postcranial skeleton of Simocyon batalleri (Viret, 1929) (Carnivora, Ailuridae) from the Late Miocene of Spain

We describe the postcranial anatomy of the Miocene puma-sized ailurid Simocyon batalleri , discussing some aspects of its biomechanics and inferring a probable life style. The postcranial anatomy of S. batalleri was previously unknown due the fragmentary nature of its fossil record, and most of the available fossils corresponded to cranial and dental material. With the discovery of a rich sample from the Late Miocene natural trap of Batallones-1, to the south of Madrid (Spain), including the remains of at least two individuals of S. batalleri , it is possible to study for the first time the anatomy of the cervical and lumbar vertebrae, complete forelimb and partial hind limb. The morphology of the forelimb, the lumbar region and the unexpected presence of a false-thumb are strongly suggestive of arboreal capabilities. Such locomotor abilities are consistent with a palaeobiological model of a generalized carnivore that foraged mainly on the ground but could readily climb to trees for safety if faced with the threat of larger competing carnivores.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 593–621.     

Systematic and comparative anatomy of Maxillarieae (Orchidaceae), sans Oncidiinae

On the basis of floral and vegetative morphology, 63 tropical American genera have been recognized within Maxillarieae. We were able to examine anatomical material of all subtribes, excluding Oncidiinae. Stegmata with conical silica bodies occur in leaves and stems of all subtribes excluding Ornithocephalinae, and pericyclic stegmata found in roots are characteristic of Lycastinae. Lycastinae and Maxillariinae are characterized by foliar glands, foliar fibre bundles and tilosomes. Endodermal cells are U-thickened in most Zygopetalinae; O-thickened in most Lycastinae, Ornithocephalinae and Telipogoninae; variously thickened in Maxillariinae; and thin-walled in Cryptarrhena lunata . Water-storage cells varied from thin-walled to variously banded throughout Maxillarieae. Cladistic analyses using anatomical characters yielded no resolution among subtribes, illustrating that anatomical characters are of limited value in assessing relationships within this tribe.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 251–274.     

Molecular phylogeny and zoogeography of the freshwater crayfish genus Cherax Erichson (Decapoda: Parastacidae) in Australia

The evolutionary history and biogeography of freshwater-dependent taxa in Australia is of intrinsic interest given the present-day aridity of this continent. Cherax is the most widespread and one of the most species-rich of Australia's nine freshwater crayfish genera. The phylogenetic relationships amongst 19 of the 23 Australian Cherax were established from mitochondrial DNA sequences representing the 12S rRNA and 16S rRNA gene regions. The relationships among species support an initial east–west separation, followed by a north–south divergence in eastern Australia. Molecular clock estimations suggest that these divergences date back to the Miocene. The phylogenetic relationships support endemic speciation within geographical regions and indicate that long-distance dispersal has not led to recent speciation as previously hypothesized. This new evolutionary scenario is consistent with the climatic history of Australia and the evolutionary history of other similarly distributed freshwater-dependent organisms in Australia.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 553–563.     

Fruit and seed ontogeny related to the seed behaviour of two tropical species of Caesalpinia (Leguminosae)

Caesalpinia echinata and C. ferrea var. ferrea have different seed behaviours and seed and fruit types. Comparison of the seed ontogeny and anatomy partly explained the differences in seed behaviour between these two species of Brazilian legumes; some differences were also related to fruit development. The seed coat in C. ferrea consisted of two layers of osteosclereids, as well as macrosclereids and fibres, to form a typical legume seed coat, whereas C. echinata had only macrosclereids and fibres. In C. echinata , the developing seed coat had paracytic stomata, a feature rarely found in legume seeds. These seed coat features may account for the low longevity of C. echinata seeds. The embryogeny was similar in both species, with no differences in the relationship between embryo growth and seed growth. The seeds of both species behaved as typical endospermic seeds, despite their different morphological classification (exendospermic orthodox seeds were described for C. echinata and endospermic orthodox seeds for C. ferrea ). Embryo growth in C. ferrea accelerated when the sclerenchyma of the pericarp was developing, whereas embryonic growth in C. echinata was associated with the conclusion of spine and secretory reservoir development in the pericarp. Other features observed included an endothelial layer that secreted mucilage in both species, a nucellar summit, which grew up into the micropyle, and a placental obturator that connected the ovarian tissue to the ovule in C. ferrea . © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 57–70.     

A new dwarf boa (Serpentes, Booidea, 'Tropidophiidae') from the Early Oligocene of Belgium: a case of the isolation of Western European snake faunas

Falseryx neervelpensis sp. nov. (Booid-grade, 'Tropidophiidae') from the earliest Oligocene (MP 21) of Belgium is described on the basis of vertebrae coming from all major portions of the vertebral column. In its peculiar caudal osteology, the snake approaches the unique morphological pattern characteristic of the living Neotropical Tropidophiinae. This is the first time such a complete and informative vertebral column of a dwarf boa has been described. The genus Falseryx was absent from Western Europe in younger parts of the Oligocene, but reappeared at the end of the Early Miocene. This dispersal pattern provides additional evidence that in most phases of the Oligocene and Early Miocene Western European snake faunas were effectively isolated from possible influences from the East.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 393–406.     

The morphology and relationships of the Sphaerosepalaceae (Malvales)

The comparative vegetative and reproductive morphology and anatomy of the Malagasy endemic family Sphaerosepalaceae is examined in light of two current competing hypotheses of relationship from recent molecular studies. Sphaerosepalaceae are similar to Thymelaeaceae on the basis of leaf architecture, calyx vasculature and in having endostomal micropyles. Comparisons with Tepuianthus and Thymelaeaceae subfamily Octolepidoideae are drawn on the basis of seed structure, indument type, perianth structure and pollen. Resin-filled, sclerenchymatous idioblasts, floral (positional) monosymmetry, a single series of stamen trunk bundles and a well-developed bixoid chalaza in the seed of Dialyceras parvifolium link Sphaerosepalaceae with its other putative sister group: a clade containing Bixaceae, Cochlospermaceae and Diegodendraceae. Synapomorphies of Sphaerosepalaceae include: fused, intrapetiolar stipules, embryo structure, pollen with endoapertures encompassing the ectoapertures and a tetramerous perianth. The extremely well-developed apical septum in the eusyncarpous gynoecium of Rhopalocarpus suggests that the gynoterminal style present in this genus has been secondarily derived from an ancestor with a fully syncarpous, basistylous gynoecium, as in Dialyceras . The morphological and evolutionary nature of basistylous and apically septate gynoecia is discussed. A rosette arrangement of ovules in each carpel coccus of D. coriaceum expands the bauplan concept of Sphaerosepalaceae and is probably unique among angiosperms as a whole.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 1–40.     

Patagial complex evolution in hummingbirds and swifts (Apodiformes): a molecular phylogenetic perspective

Studies of the role of flight in vertebrate evolution often have focused on the propatagial muscle complex because this structure forms the wing's leading edge. However, historical narratives about the evolution of flight anatomy are compromised because traditional higher-level taxonomies typically are based in part on the propatagium itself. To avoid this circularity, I used a consensus molecular phylogeny to examine propatagial evolution in the highly aerial sister groups, hummingbirds and swifts (Apodiformes). Mapping of anatomy on molecular-based phylogeny indicates that structural variation in M .  tensor propatagialis pars brevis (TPB) is congruent with the major subclades of both hummingbirds and swifts. However, the humeral tendon and broad attachment of the fleshy belly of TPB with M .  extensor metacarpi radialis (EMR) most likely underwent parallel change in hummingbirds and swifts, while the distal tendon present only in hummingbirds changed from a thin sheet to a strong tendon. The combination of divergent (within hummingbirds or swifts) and parallel (between hummingbirds and swifts) evolutionary patterns implies that the taxonomic value of the propatagial complex in apodiformes depends on anatomical component and level of divergence. The congruence of anatomy with molecular phylogeny provides independent criteria for designating relatively ancestral versus derived clades of apodiformes. Based on these polarities, living hummingbirds and swifts express additional parallel trends from arboreal to more aerial foraging styles, and from depauperate to species-rich clades. Within apodiformes, the link of flight anatomy with taxonomic and ecologic diversity suggests that elaboration of locomotor modes was important for apodiform diversification, echoing a similar pattern for birds relative to their reptilian ancestors.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 211–219.     

Logistic regression in comparative wood anatomy: tracheid types, wood anatomical terminology, and new inferences from the Carlquist and Hoekman southern Californian data set

Despite collecting copious amounts of data, wood anatomists rarely perform appropriate statistical analyses, especially in the case of categorical variables. Nevertheless, anatomists have succeeded in identifying strong ecological trends. We show that, with only a slightly more sophisticated analysis, the strength and significance of 'well-known' associations can be quantified, and new associations pinpointed. Using logistic regression to reanalyse the classic Carlquist and Hoekman data set for the southern Californian flora, we show strong support for the notion that true tracheid presence lowers vessel grouping; in contrast, vasicentric tracheids are associated with a diversity of vessel grouping strategies. We show that statistical models can refine anatomical interpretations by identifying unusual species. For example, Fremontodendron californicum and Baccharis salicifolia (=  B. glutinosa ) were identified as unusual in lacking vasicentric tracheids; a consultation of preparations revealed that they are indeed present. For purposes of ecological wood anatomy, anatomical terminology should reflect cell function; we suggest that terminological systems that yield better predictive power in statistical models such as ours are preferable. Finally, we make recommendations ranging from the statistical, e.g. the need to check assumptions and the need for the inclusion of phylogeny, to the biological, e.g. gathering data expressly designed to test functional hypotheses rather than all of the information in standardized lists.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 331–351.