16 de junio de 2024

Gondwanan Relationships of the Cape

The Cape Floristic Region exhibits many correlations with the former Gondwanan landmasses. It was long thought that this was because of vicariance; the groups spread across the continents when they were connected. However, molecular clocks have indicated that the majority of dispersals occurred after the continents split, indicating overseas dispersal. The continents would have still been closer together at the time, so spreading would be easier than today. Note that all Gondwanan angiosperm groups are probably overseas dispersers, as most of angiosperm evolution only occurred after Gondwana split.

There are three main Gondwanan realms: South America, Africa and Australasia (including their offshore islands). Antarctica was also a member, but today it is so sterilized that little evidence of its Gondwanan affinities remain among the extant species. The Indian Subcontinent was also once connected to Madagascar and Africa, but a combination of volcanic activity in the Cretaceous and its collision with Asia has wiped out most of its Gondwanan groups, though several interesting ones remain. The main Gondwanan sub-realms (those with distinct biota) are Southern South America, Southern Africa, Madagascar, Australia, New Guinea, New Caledonia and New Zealand.

South America and Australasia have a closer relationship than with Africa. Numerous Gondwanan groups (e.g. Araucariaceae, Nothofagaceae, Gripopterygidae) are found in South America and Australasia but not Africa. This is sometimes explained by Africa being the furthest north and these groups becoming extinct here due to the warmer climate. But considering all three groups I mentioned back there actually occur well into the tropics, this explanation is not very satisfactory. The Cape seems to have a much stronger relationship with Australasia than to South America.

I will list all of the groups in the Cape with Gondwanan relationships I know of. Groups can be monophyletic (a Gondwanan clade) or paraphyletic (the group's basal branches are Gondwanan, with the apical branches spreading north, indicating the group was fully Gondwanan in the past). I do not include groups that have obviously spread very recently (around the last 5 million years).

Pan-Gondwanan Relationships

These groups have widespread relationships among the Gondwanan realms. Some pan-Gondwanan groups (like Restionaceae and Proteaceae) are included in other sections, due to the relationship being much stronger between the Cape and one other realm than to the others.

Afrotheria (Mammalia: Placentalia) - A very morphologically diverse group of mammals that originated in Africa during the Cretaceous. The basal mammal clades (those excluding Boreotheria) are all associated with the southern continents: Monotremata (Australasia), Marsupialia (Australasia and South America), Xenarthra (South America), Afrotheria (Africa). This indicates the mammals may have initially diversified in Gondwana during the Mesozoic. Afrotheria has since spread across the world by land and sea, but the vast majority of species are in Sub-Saharan Africa.

Palaeognathae (Reptilia: Aves) - Ground birds distributed in South America, Africa, Australia, New Guinea, New Zealand and until recently, Madagascar. The nature of their dispersal is controversial, but molecular clock indicates it is of a Cenozoic overseas nature.

Galaxiidae (Actinopterygii: Galaxiiformes) - Primarily freshwater fish found in Southern South America, the South African Cape, Australia, New Caledonia and New Zealand. Molecular clock indicates a Cenozoic overseas dispersal. Given that some species spend their youth at sea (none in the Cape), this is a very plausible explanation.

Micropterigidae (Insecta: Lepidoptera) - The most basal family of Lepidoptera, these unusual mandibulate moths are found around the world but are split into two perfectly hemisphere-segregated clades. The Southern Hemisphere clade includes species from South America, South Africa, Australia, New Caledonia and New Zealand. Fossils indicate the group originated shortly after the origin on the Lepidoptera around the beginning of the Jurassic.

Barbarochthonidae (Insecta: Trichoptera) - Family of caddisflies endemic to pristine streams in the South African Cape. They are sister to the Helicophidae of Southern South America and Australasia. With a split dated to the Late Cretaceous, the relationship may just possibly be vicariant.

Chironomidae (Insecta: Diptera) - Very common midges found worldwide with aquatic or semi-aquatic larvae. The subfamily Aphroteniinae is limited to Southern South America, the South African Cape and Australia (the Cape's only genus, Aphrotenia, is also present in Australia). The Cape-endemic genus Elpiscladius, from the Orthocladiinae, may have affinities with the South American/Australian genus Austrobrillia.

Stolotermitidae (Insecta: Blattodea) - Basal family of termites found in Southern South America, the South African Cape, Australia and New Zealand. The genus Stolotermes is limited to the Cape, Australia and New Zealand.

Anostostomatidae (Insecta: Orthoptera) - Well-known family of Ensifera that is found across much of the world, but with a diversity greatly skewed to the southern continents.

Notonemouridae (Insecta: Plecoptera) - Stoneflies found in pristine, cool streams and important indicators for Southern Hemisphere rivers. Found in Southern South America, Southern Africa, Madagascar, Australia and New Zealand. Phylogeny and fossils indicate a traditional, vicariant dispersal in the Jurassic period. This is probably the most widespread family of insects (or any other group) endemic to the Southern Hemisphere.

Archaeidae (Arachnida: Araneae) - Odd family of spiders found in South Africa, Madagascar and Australia. Fossils indicate a former Laurasian presence but they may still have originated in the Southern Hemisphere.

Peripatopsidae (Panarthropoda: Onychophora) - Velvet worms found in Southern South America, the South African Cape, Australia, New Guinea and New Zealand. Molecular clock indicates this group dispersed by vicariance. The Australasian genera split off in the Triassic period and the South American and African genera split in the Jurassic.

Cupressaceae (Pinopsida: Cupressales) - Ancient group of conifers found across the world. The subfamily Actinostroboideae is distributed in Southern South America, Southern Africa, Australia, New Guinea, New Caledonia and New Zealand. Molecular clock indicates most of the dispersal took place in the Cretaceous, which would indicate a mix of overland and short-distance overseas dispersal.

Podocarpaceae (Pinopsida: Araucariales) - Broad-leaved conifers found across much of the world, but very skewed towards the southern continents. They are found in the American Tropics, Africa, Madagascar, Tropical Asia, Australia, New Guinea, New Caledonia and New Zealand. Molecular clock indicates a Cenozoic overseas dispersal.

South American Relationships

These groups have specific relationships between the Cape and South America. I have found there to be not as many as one might expect.

Sericostomatidae (Insecta: Trichoptera) - Caddisflies found across most of the world apart from Australasia. Their phylogenetic position indicates an African origin in the Cretaceous. The basal-most genera are found in the Cape or Madagascar, with the next most basal genera being South American, indicating an initial Gondwanan spread west. From there, the genera spread to North America and much of the world, but stopped at Australasia, possibly due to competition from pre-established endemic Sericostomatoid families.

Paraphrynoveliidae - (Insecta: Hemiptera) - Facultatively semi-aquatic bugs limited to the mountains of the Cape and the Drakensberg. They are sister to the New World family Macroveliidae (which they have been proposed to be merged with by one author). The basal-most member of Macroveliidae is found in Southern South America, indicating a Gondwanan base to the broader group.

Thurniaceae (Monocots: Poales) - Aquatic reedy plants distributed in South America and parts of South Africa (Cape and Pondoland only).

Bruniaceae (Eudicots: Bruniales) - Family of ericoid plants endemic to the fynbos-type vegetation of South Africa. They are sister to the Columelliaceae of South America, and the two families form the Gondwanan order Bruniales.

Australasian Relationships

These groups have specific relationships between the Cape and Australasia (Australia, New Guinea, New Caledonia, New Zealand). The relationship between the Cape and Australia is particularly close, possibly due to their similar climates. Both regions have their own small floral kingdoms.

Pisuliidae (Insecta: Trichoptera) - Caddisflies native to Africa and Madagascar. They are sister to the Australasian-endemic families Plectrostarsidae + Oeconescidae. The outgroup to these three is the Kokiriidae, found in Australasia and South America. Molecular clock indicates a mid-Cretaceous split, just possibly vicariant.

Hydrosalpingidae (Insecta: Trichoptera) - Caddisflies endemic to pristine streams in the South African Cape. They are sister to the Australian-endemic family Heloccabusidae. The split was likely Cenozoic, indicating an overseas dispersal. The outgroups are also Australasian, indicating a Australasia-to-Africa spread.

Nemopteridae (Insecta: Neuroptera) - Lacewings known for their impressively-modified hindwings. Despite being quite widespread, over half of all species are endemic to Southern Africa. The Australian-endemic genus Chasmoptera is sister to a group containing the Southern African genera Nemeura, Semirhynchia and Sicyoptera. The split, dated to the mid-Cretaceous, may possibly be vicariant.

Sialidae (Insecta: Megaloptera) - Known as alderflies, these insects have aquatic larvae. The South African-endemic genus Leptosialis is sister to the Australian-endemic genus Stenosialis. More broadly, the basal branches of the Sialidae are all Gondwanan, distributed in Australasia, South Africa, Madagascar, India and South America with only the apical branches being in the northern continents.

Cicadellidae (Insecta: Hemiptera) - Small plant bugs found worldwide. The peculiar tribe Cephalelini is limited to the South African Cape, Australia and New Zealand and is exclusively associated with Restionaceae plants. Molecular clocks indicate a Australasia-to-Africa, Cenozoic overseas dispersal. Their absence from South America may be due to how recently the Restionaceae arrived on that continent.

Phlaeothripidae (Insecta: Thysanoptera) - Family of thrips found worldwide. The genus Jacotia is oddly limited to just the South African Cape and Australia.

Libelluloidea (Insecta: Odonata) - Numerous genera in this superfamily of dragonflies remain unplaced to family. The South African-endemic genus Syncordulia may have affinities to some Australian genera, but research on the topic has been very slow.

Restionaceae (Monocots: Poales) - Distinctive, reedy plants distributed in Southern South America, Africa, Madagascar, Australasia and even Southeast Asia (just one species; the family's only presence in the Northern Hemisphere). However, diversity is enormously skewed to the South African Cape and Australia. The family dominates the landscape in parts of the two places, while they are only a minor component everywhere else. In fact, all Restionaceae genera are found either in the Cape or Australia, but some may be found in other regions in addition to one of those two locations. Their presence in South America is very recent, as indicated by South America sharing both its genera with Australasia. Phylogenetics indicates a Cenozoic overseas dispersal in an Australasia-to-Africa direction.

Lanariaceae (Monocots: Asparagales) - Family endemic to Cape fynbos. Phylogenetics show it is descended from the group that includes the Australian endemic families Blandfordiaceae and Boryaceae. The apex of this group includes spreads to South America/Australasia (Asteliaceae) and worldwide (Hypoxidaceae).

Proteaceae (Eudicots: Proteales) - Morphologically diverse trees or shrubs, generally with distinctive inflorescences. Distributed in South America, Africa, Madagascar, Australasia and Tropical Asia but diversity is by far the greatest in the South African Cape and Australia. Other regions do have their own genera, however. The family dominates some landscapes in the Cape and Australia, but is much rarer elsewhere. Fossils and molecular clocks indicate the group originated in Australasia and spread to Africa several times overseas during the Cenozoic.

Geissolomataceae (Eudicots: Crossosomatales) - Family endemic to Cape fynbos. Found on a three-family branch of its order limited to the Southern Hemisphere. Its sister is the Strasburgeriaceae of New Zealand and New Caledonia. The outgroup, Aphloiaceae, is from the East Africa/Madagascar region, indicating this is an unusual case of Africa-to-Australasia dispersal.

Zamiaceae (Cycadopsida: Cycadales) - Cycads only barely qualify as a Cape group, just making it into the eastern edge of the Cape Floristic Region. The only genus in the Cape, Encephalartos, mostly found in tropical Africa, is nested in a group of otherwise Australian genera. The dispersal from Australasia to Africa probably occurred around the end of the Cretaceous, and therefore was probably overseas.

Malagasy/Indian Relationships

These groups have specific relationships between the Cape, Madagascar and/or the Indian Subcontinent. The Cape shares quite a few species with Madagascar, but most of these are very recent dispersals that don't really qualify as Gondwanan. Ancient and probably ancient groups are included. Despite having a reduced Gondwanan biota, India does share numerous groups with Madagascar, reflecting their connection as a single island until the Cretaceous.

Petrothrincidae (Insecta: Trichoptera) - Yes, I do read a lot about caddisflies. This family is associated with pristine streams in the South African Cape and Madagascar. The measured mid-Cretaceous split may just possibly mean a vicariant dispersal. A related family, Ceylanopsychidae, is endemic to Sri Lanka but has not been included in any phylogenies. Similar designs in the case between these two families may indicate that they are related.

Hydraenidae (Insecta: Coleoptera) - Tiny aquatic or semi-aquatic beetles found worldwide, but much more diverse in the Southern Hemisphere. Two of the four subfamilies are endemic to the southern continents: Prosthetopinae in the Sub-Saharan Africa/Madagascar region and Orchymontiinae in New Zealand. The Malagasy Prosthetopine genus Sicilicula split from the African ones in the early Cenozoic, indicating overseas dispersal. Other Malagasy Hydraenidae bare closer affinities to India, including shared genera.

Blaberidae (Insecta: Blattodea) - Diverse cockroaches found around the world. The genus Aptera has a peculiar distribution of only South Africa and India. This may be a case of vicariance, with some molecular clocks placing the origin of Blaberidae before the Gondwanan breakup.

Teloganodidae (Insecta: Ephemeroptera) - Mayflies with nymphs that are found only in pristine streams in the South African Cape, Madagascar and Southern Asia. It is thought the group existed in the Africa/Madagascar/India region before they separated. After India's collision with Asia, some spread to Southeast Asia.

Heptageniidae (Insecta: Ephemeroptera) - Mayflies found around the world. The genus Afronurus is found in Africa, Madagascar and Southern Asia, possibly indicating a Gondwanan distribution.

Publicado el junio 16, 2024 06:27 TARDE por davidklop davidklop | 0 comentarios | Deja un comentario