Chapter

Insularity and Its Effect on Mammal Evolution

Chapter · January 1977with 81 Reads
DOI: 10.1007/978-1-4684-8851-7_23
Publisher: 0258-1221
Abstract
When the car ferry “Rethymnon” sails from Piraeus towards Crete one can already feel the strong endemic atmosphere of the island. Rethymnon itself is a beautiful historical town on Crete in an area containing many Pleistocene fossil mammal localities which have yielded endemic deer, elephants and murids. A striking thing on board the ferry are notices written in Japanese which suggest that the ship was probably not launched under the name Rethymnon and served in her earlier days on the Japanese islands. For a paleontologist this is a remarkable coincidence since the Pleistocene of Japan has also yielded unbalanced endemic faunas with a very uniform composition of elephant and deer like the fauna of Crete.

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  • ... (Hawks 2016, final paragraph). In addition to dwarfism, the development of limb shortening and of low­ gear locomotion is another island adaptation seen in larger mammals (Sondaar 1977;Van der Geer et al. 2010;Van Heteren 2012). ...
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    Deciphering the mechanisms that underlie morphological and functional diversity is essential for understanding how organisms adapt to their environment. Interestingly, phenotypic divergence does not necessarily correspond to the geographic and genetic separation between populations. Here, we explored the morphological and functional divergence among populations of two genetically differentiated clades of the Moorish gecko, Tarentola mauritanica. We used linear and geometric morphometrics to quantify morphological variation and investigated how it translates into biting and CLIMBING PERFORMANCE, to better understand the mechanisms potentially underlying population and lineage divergence. We found marked morphological differences between clades, both in body size and head shape. However, much of this differentiation is more strongly related to local variation between populations of the same clade, suggesting that recent ecological events may be more influential than deep evolutionary history in shaping diversity patterns in this group. Despite a lack of association between morphology and functional diversification in the locomotor system of the Moorish gecko, straightforward links are observed between head morphology and biting performance, providing more hints on the possible underlying causes. Indeed, variation in bite force is mostly determined by size variation and sexual dimorphism, and differences between the two clades concern how sexual variation is expressed, reinforcing the idea that both social and ecological factors contribute in shaping differentiation. Interestingly, the individuals from the islets off the coast of Murcia exhibit particular morphological and functional traits, which suggests that the ecological conditions related to insularity may drive the phenotypic differentiation of this population.
  • ... Many native species evolved without natural predators and lost anti-predator stra- tegies, such as fight and flee responses, high reproduction levels, ste- reoscopic view (overview in van der Geer et al., 2010) and several species developed in response a low-gear locomotion (e.g. Sondaar, 1977;van der Made, 1999van der Made, , 2005). Islanders might, on average, also be more prone to succumb to alien diseases, because of their evolution in relatively safe isolation, protected by water barriers (Duffy and Vargas, 2018). ...
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  • ... The palaeontological excavations on Crete, mainly in coastal caves, reveal the presence of two main Pleistocene (Last Ice Age) biozones (Dermitzakis and de Vos, 1978;Mayhew, 1996). The first and oldest biozone is dated to the Early Middle Pleistocene, is characterized by a typical island fauna lacking terrestrial predators and poor overseas colonizers (Sondaar, 1977) and consisted exclusively of giant mice (Kritimys catreus, K. kiridus), a dwarf mammoth (Mammuthus creticus) and a dwarf hippopotamus (Hippopotamus creutzburgi). The second biozone, ranging from the Middle Pleistocene to the end of the Late Pleistocene, is characterized by a similarly distinctive endemic fauna that differs in composition from that of the previous period. ...
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  • ... Estas tendencias evolutivas son resultado de presiones de selección similares bajo condiciones ecológicas parecidas, y determinadas por el régimen de insularidad. Esto implica una reducción de la disponibilidad de los recursos trófi cos, un aumento de las presiones de competencia intra-e interespecífi ca, y una baja presión de depredación, y generalmente resulta, al menos en los mamíferos, en una optimización de los recursos energéticos, mediante cambios en el tamaño corporal y adaptaciones particulares del aparato locomotor, del aparato masticatorio, del sistema nervioso y/o de la historia vital (e.g., Sondaar, 1977;Alcover et al., 1981;Lomolino, 2005;Köhler & Moyà-Solà, 2004, 2009. ...
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  • ... This latter scenario would be legitimate and plausible based on the archaeologi- cally documented fact that domesticated animals went through a gradual size decrease follow- ing their initial management beginning around 10th millennium BC in southwest Asia ( [6] and references therein) and references therein). Furthermore, the fact that island faunas go through rapid size reduction due to genetic bottle-necks created by island insularity phenome- non (sensu [78]) represents an opportunity to test whether G?k?eada assemblages show the effects of this phenomenon, or instead, they display affinities with the mainland as a result of the colonization. It is of particular interest to test whether the pace and magnitude of size decrease increased or decreased after the initial Neolithic colonization. ...
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  • ... Such studies are important because they demonstrate substantial morphological variation among isolated but closely located populations. The evolution of animals on islands has long been of great interest for researchers (e.g., Darwin, 1845;MacArthur and Wilson, 1967;Sondaar, 1977;Lomolino, 2005) since evolutionary changes may happen much more rapidly in isolated island populations (Millien, 2006). Morphological differentiation among populations can indeed be influenced by several evolutionary mechanisms, including gene flow, genetic drift, and adaptation to local environmental conditions (Foster, 1964;Pergams and Ashley, 2001;Losos and Ricklefs, 2009). ...
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  • ... Today, most of these island endemics are extinct and are known to us only by their fossil remains ( Alcover et al., 1998). The larger insular mammals present unique adaptations to the island environment compared to their mainland relatives, such as smaller size combined with robust and short limbs ( Sondaar, 1977;Sondaar and Van der Geer, 2005). A difficulty in the study of these mammals is that they are so highly adapted to their new environment; it is not easy to trace their direct mainland ancestor. ...
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