The study of morphology has always had a fundamental role in several fields of natural sciences, like taxonomy and geographic variation. During the 20th century, morphological studies have developed towards more rigorous traditional morphometric analyses and even further, to the last advances of geometric morphometrics. These new techniques allow scientists to test biological hypotheses on shape and size variation through a set of powerful statistical and graphic tools. Morphometrics still plays a relevant role in depicting adaptive and functional interpretations of geographic variation and macro- and micro-evolutionary pathways, thus offering a fruitful contribution in the identification of Management Units for Conservation plans. I applied two-dimensional geometric morphometrics to study the mandibular form of wide-ranging mammals of conservation concern: the closely related dolphins Stenella coeruleoalba (Meyen, 1833), Delphinus delphis Linnaeus, 1758, Tursiops truncatus (Montagu, 1821) and the brown bear Ursus arctos Linnaeus, 1758. Main aim was to evaluate the mandibular form’s effectiveness in recognizing taxonomic units and identifying its adaptive and phylogenetic constraints at the inter and intraspecific scale. In the first two articles, I analysed interspecific mandibular variation and modularity in the three dolphin species, first within the Mediterranean Sea and then extending the sampling to the Atlantic waters. The odontocete lower jaw is divided into two distinct modules: the ramus and the corpus which likely reflect a functional separation corresponding to the hearing and the feeding functions. In the Mediterranean Sea, the species were clearly differentiated in the mandibular foramen, the only diagnostic taxonomic character. The Mediterranean subpopulations discriminated from the Atlantic ones, and different patterns of phenotypic change were observed across the geographic gradient in T. truncatus with respect to the other two species. In the third article, I evaluated the phylogenetic component of odontocete mandibular form and reconstructed its ancestral shape and size to analyse trait evolution across the clade. The mandibular shape evolved under the action of selective pressures and a significant phylogenetic signal in the family Delphinidae was detected in shape but not in size. Ancestral mandibular reconstruction corresponded to that of a generalist feeder and evolved across the clade toward more specialized suction and raptorial feeder’s traits. In the last chapter, I concentrated on the family Ursidae and on the geographic variability of the brown bear to identify the impact of taxonomy, climate and size on mandibular shape variation. Both size and shape data were useful characters to discriminate extant bears species with very high percentage of accuracy. The subspecies U. a. isabellinus and U. a. marsicanus have distinct morphologies from all other brown bear populations. These taxa exhibit a high degree of morphological differentiation possibly because of a long process of isolation. The mandible proved to be an informative skull element and confirmed its effectiveness in sorting out evolutionary relationships within a clade, finding diagnostic traits for taxonomic investigations as well as contributing to the identification of distinct populations that could deserve specific resources in terms of conservation effort, as in the case of the brown bear and of the Mediterranean dolphins. This research would not have been possible without the EC-funded SYNTHESYS project, College Italia and Erasmus Placement projects and without the support of the University of Molise that allowed the visit of Natural History Museum collections of Stockholm, Copenhagen, Edinburgh, Liverpool and New York. Therefore, I would like to stress the importance of museum collections that, ever since they became established in the 19th century, still have a fundamental value in preserving specimens and guaranteeing their availability for scientific research.
Lo studio della morfologia ha sempre avuto un ruolo fondamentale in molti ambiti delle scienze naturali, come nella tassonomia e nello studio della variabilità geografica. La morfometria geometrica permette di indagare la variazione di taglia e forma attraverso efficaci mezzi grafici e statistici, contribuendo all’identificazione e all’interpretazione di pattern di variabilità fenotipica sia a livello microevolutivo che macroevolutivo. In questo progetto di ricerca ho applicato le tecniche della morfometria geometrica bidimensionale per studiare la morfologia della mandibola in mammiferi ad ampia distribuzione di particolare interesse conservazionistico: tre delfini Stenella coeruleoalba (Meyen, 1833), Delphinus delphis Linnaeus, 1758, Tursiops truncatus (Montagu, 1821) e l’orso bruno Ursus arctos Linnaeus, 1758. Il principale scopo è quello di verificare se lo studio della morfologia mandibolare sia efficace nel riconoscere le unità tassonomiche e nell’identificarne le componenti adattative e filogenetiche, sia a livello intraspecifico sia interspecifico. Nei primi due articoli della tesi, ho analizzato la variabilità interspecifica in tre specie di delfini provenienti dal Mare Mediterraneo e dall’oceano Atlantico. La mandibola dei delfini è suddivisa dal punto di vista morfologico in due moduli corrispondenti al ramo e al corpo, che potrebbero riflettere a loro volta una separazione sul piano funzionale corrispondente alle aree adibite all’udito e all’alimentazione. Il foramen mandibolare ha inoltre permesso di distinguere chiaramente le tre specie, essendo l’unico carattere diagnostico per il riconoscimento interspecifico. Le popolazioni Atlantiche si discriminano da quelle Mediterranee e i pattern di variazione fenotipica attraverso il gradiente geografico sono diversi nel tursiope rispetto alle altre due specie. Nel terzo articolo ho preso in considerazione la componente filogenetica della mandibola degli odontoceti, ricostruendone la forma ancestrale al fine di analizzare la sua evoluzione attraverso il clade, testando al contempo se la variazione morfologica sia stata soggetta a pressioni selettive. La forma della mandibola si è evoluta sotto l’azione di pressioni selettive e un segnale filogenetico significativo è stato individuato nella forma ma non nella taglia. La ricostruzione della forma ancestrale è relazionabile a una dieta generalista che si è evoluta nel tempo verso diete più specializzate. L’ultimo capitolo riguarda la famiglia Ursidae e, in particolare, la variabilità morfologica dell’orso bruno, e ha l’obiettivo di identificare l’influenza della tassonomia, del clima e della taglia sulla variabilità della forma mandibolare. La mandibola, nelle sue componenti di forma e taglia, è in grado di distinguere le specie con un’elevata percentuale di accuratezza. Inoltre, le due sottospecie Ursus arctos isabellinus e Ursus arctos marsicanus sono risultate essere chiaramente discriminate rispetto alle altre popolazioni di orso bruno, probabilmente come risultato di un lungo processo di isolamento. La mandibola, nonostante la sua semplicità strutturale, è risultata essere una componente cranica estremamente informativa e ha confermato la sua efficacia nel mettere in luce le relazioni evolutive di un clade, nell’identificare tratti anatomici diagnostici utili nelle indagini tassonomiche, così come nel contribuire al riconoscimento di popolazioni distinte che potrebbero necessitare di specifiche strategie di conservazione, come nel caso dell’orso bruno marsicano o delle popolazioni di delfini mediterranei. La presente ricerca non si sarebbe potuta realizzare senza il sostegno dei seguenti fondi: SYNTHESYS project della Comunità Europea, College Italia, Erasmus Placement projects e senza il supporto dell’Università degli Studi del Molise che ha permesso la visita alle collezioni di storia naturale nei musei di Stoccolma, Copenhagen, Edimburgo, Liverpool e New York.
Geometric morphometrics and conservation of wide ranging mammals. Identifying Management Units and Evolutionary Significant Units in the brown bear Ursus arctos and in three Mediterranean Dolphins (Stenella coeruleoalba, Delphinus delphis, Tursiops truncatus)
GUIDARELLI, Giulia
2017-05-22
Abstract
The study of morphology has always had a fundamental role in several fields of natural sciences, like taxonomy and geographic variation. During the 20th century, morphological studies have developed towards more rigorous traditional morphometric analyses and even further, to the last advances of geometric morphometrics. These new techniques allow scientists to test biological hypotheses on shape and size variation through a set of powerful statistical and graphic tools. Morphometrics still plays a relevant role in depicting adaptive and functional interpretations of geographic variation and macro- and micro-evolutionary pathways, thus offering a fruitful contribution in the identification of Management Units for Conservation plans. I applied two-dimensional geometric morphometrics to study the mandibular form of wide-ranging mammals of conservation concern: the closely related dolphins Stenella coeruleoalba (Meyen, 1833), Delphinus delphis Linnaeus, 1758, Tursiops truncatus (Montagu, 1821) and the brown bear Ursus arctos Linnaeus, 1758. Main aim was to evaluate the mandibular form’s effectiveness in recognizing taxonomic units and identifying its adaptive and phylogenetic constraints at the inter and intraspecific scale. In the first two articles, I analysed interspecific mandibular variation and modularity in the three dolphin species, first within the Mediterranean Sea and then extending the sampling to the Atlantic waters. The odontocete lower jaw is divided into two distinct modules: the ramus and the corpus which likely reflect a functional separation corresponding to the hearing and the feeding functions. In the Mediterranean Sea, the species were clearly differentiated in the mandibular foramen, the only diagnostic taxonomic character. The Mediterranean subpopulations discriminated from the Atlantic ones, and different patterns of phenotypic change were observed across the geographic gradient in T. truncatus with respect to the other two species. In the third article, I evaluated the phylogenetic component of odontocete mandibular form and reconstructed its ancestral shape and size to analyse trait evolution across the clade. The mandibular shape evolved under the action of selective pressures and a significant phylogenetic signal in the family Delphinidae was detected in shape but not in size. Ancestral mandibular reconstruction corresponded to that of a generalist feeder and evolved across the clade toward more specialized suction and raptorial feeder’s traits. In the last chapter, I concentrated on the family Ursidae and on the geographic variability of the brown bear to identify the impact of taxonomy, climate and size on mandibular shape variation. Both size and shape data were useful characters to discriminate extant bears species with very high percentage of accuracy. The subspecies U. a. isabellinus and U. a. marsicanus have distinct morphologies from all other brown bear populations. These taxa exhibit a high degree of morphological differentiation possibly because of a long process of isolation. The mandible proved to be an informative skull element and confirmed its effectiveness in sorting out evolutionary relationships within a clade, finding diagnostic traits for taxonomic investigations as well as contributing to the identification of distinct populations that could deserve specific resources in terms of conservation effort, as in the case of the brown bear and of the Mediterranean dolphins. This research would not have been possible without the EC-funded SYNTHESYS project, College Italia and Erasmus Placement projects and without the support of the University of Molise that allowed the visit of Natural History Museum collections of Stockholm, Copenhagen, Edinburgh, Liverpool and New York. Therefore, I would like to stress the importance of museum collections that, ever since they became established in the 19th century, still have a fundamental value in preserving specimens and guaranteeing their availability for scientific research.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
