Allochronic taxa as an alternative model to explain circumantarctic disjunctions

Abstract

Most biogeographical studies propose that southern temperate faunal disjunctions are either the result of vicariance of taxa originated in Gondwana or the result of transoceanic dispersal of taxa originated after the breakup of Gondwana. The aim of this paper is to show that this is a false dichotomy. Antarctica retained a mild climate until mid-Cenozoic and had lasting connections, notably with southern South America and Australia. Both taxa originally Gondwanan and taxa secondarily on Gondwanan areas were subjected to tectonicinduced vicariance, and there is no need to invoke ad hoc transoceanic dispersal, even for post-Gondwanan taxa. These different elements with circumantarctic distributions are here called 'allochronic taxa' -taxa presently occupying the same area, but whose presence in that area does not belong to the same time period. This model allows accommodation of conflicting sources of evidence now available for many groups with circumantarctic distributions. The fact that the species from both layers are mixed up in the current biodiversity implies the need to use additional sources of evidence -such as biogeographical, palaeontological, geological and molecular -to discriminate which are the original Gondwanan and which are post-Gondwanan elements in austral landmasses.

Systematics of the Neotropical caddisfly genus Notidobiella Schmid (Trichoptera, Sericostomatidae), with the description of 3 new species

“…This “transantarctic exchange” pattern also has been demonstrated for other insects, including aquatic taxa (Cranston and Edward 1999, Amorin et al 2009, Daugeron et al 2009). However, it may be that the current distribution of other southern Gondwana caddisflies, such as Sericostomatidae, reflects an older dispersal prior to the breakup of southern Gondwana, now represented by relict Southern Hemisphere distributions.…”

Filogenia de Leiinae (Diptera, Mycetophilidae) com uma nova proposta de classificação para a subfamília

“…The final disruption between Australia and South America occurred only in the second half of the Cenozoic, about 35 mya (McLoughlin 2001), meaning that there has been a lasting connection between Australia and South America with Antarctica since the Cretaceous to the mid Cenozoic. This explains why amphinotic distributions are a widespread biogeographical pattern-and, hence, originated through vicariance, not transoceanic dispersal-but with an age of disruption not compatible with the initial division of Gondwana (Amorim et al 2009). …”

On the role of assumptions in cladistic biogeographical analyses

“…In the search for a common pattern, the addition of areagrams derived from other distinct taxa is needed, since "congruence is the main target of comparative biology" (Santos & Capellari, 2009, p. 410). Geographical congruence within two or more areagrams strongly suggests the existence of a common cause rather than numerous independent causes (Nelson & Platnick, 1981;Llorente et al, 1996;Amorim et al, 2009;Crisp et al, 2011).…”

“…Moreover, A0 is in general limited to a vicariancist perspective and it negatively influences causal interpretations of biogeographical patterns (see geodispersal of Lieberman & Eldredge, 1996, for instance). It is generally accepted among historical biogeographers that dispersal explanations should not be used as first-order biogeographical explanations (e.g., Santos, 2007a, andAmorim et al, 2009), since they are untestable individual narratives. However, to ignore dispersal a priori and to assume it a posteriori (as in Secondary BPA) seems to deny (or at least to question) the relevance of dispersal to biogeography.…”