Forest fragments became like islands in the sea
Aridification during the Plio-Pleistocene, about 5-3 million years ago in eastern Africa created large savannas, and isolated forests.
During thousands of years isolated animal and plant populations in different forest fragments began to speciate in the Eastern Arc mountains and the nearby lowland, coastal forests (Pozzi et al. 2020).
This isolation of populations led to increased number of species in all forest living animals eg. birds, frogs and primates (Colobus anglolensis and Otolemur garnettii). It also led to speciation in dwarf galagos, Paragalagos of East Africa.
Forest fragments were like islands in the sea, surrounded by dry savanna that was impenetrable for forest fauna.
Dwarf galagos, small nocturnal prosimian primates
Dwarf galagos, are nocturnal, mainly insectivorous, small (under 150 g), agile, and some species are very shy. This is why they were unknown to people even in densely populated Taita Hills for so long. Galagos are prosimians like makis in Madagasgar and tarsiers in Asia. Prosimians are primates, but they are considered to be more “primitive”. Lemurs, loris, tarsiers and galagos are prosimians.
In Africa all prosimians, different species of galagos, are nocturnal. Competition with other primate species has probably led to only nocturnal lifestyle.
Taxonomy of dwarf galagos has been a challenge for researches. These nocturnal are cryptic, meaning that many different species look the same. In the forest at night animals recognize each other by their calls, not by how they look like (Bearder, 1999).
Advertising calls, long distance contact calls are best way to identify species from another, as all species have different advertising calls. Dwarf galagos use these calls in the evenings and mornings and throughout the night for group coordination and social cohesion.
Taxonomy of these species were first based on dead individuals from museums, then recordings of their calls and other behavioral aspects including biogeographical knowledge. In last few years DNA studies have been added to previous research (Pozzi et al., 2020).
New genus – Paragalago
Dwarf galagos, genus Galagoides of Africa were recently (Masters et al., 2017) re-evaluated. This research based on genetic, vocalizations and morphological evidence divided genus Galagoides into two clades. Dwarf galagos of East Africa was given new genus Paragalago. Genus Galagoides was left for species living in western Africa. Genus Galagoides currently has three species G. demidoff, G. thomasi and G. kumbirensis. G. kumbirensis was resently described by Svensson et al., (2017) from Angola.
New genus Paragalago has, at the moment, five species. These are P. cocos, P. zanziparicus, P. granti, P. orinus and P. rondoensis. It is possible that there are more species, as many populations have been isolated for a long time. Research on Paragalagos is limited, like Taita mountain dwarf galago shows. As Taita mountain dwarf galago is possibly P. cocos Kenya coast galago (Rosti et al. 2020), this article focuses mostly for P. cocos.
Species boundaries are not simple, combination of morphological, behavioural, biogeographical, and genetic research is needed to determine species status. While all populations are important and worth conservation, knowledge about species status is important also. Conservation measures are often targeted on critically endangered species and having correct IUCN Red List conservation status may save populations from extinction.
For detailed information about all these dwarf galagos I recommend Mammals of Africa (MOA) Vol II. Vocal profiles of the species are available in Wildsolutions webpage, this is site of Eastern Africa Primate Diversity and Conservation Program lead by Thomas Butynski and Yvonne de Yong.
English names have changed eg. MOA and IUCN has different English names for these species. Thus I prefer to use Latin names.
Paragalago species ranges, English names (from IUCN 2019) and weights briefly
P. cocos: Kenya coast galago, coast of Kenya, 138-150 g.
P. zanziparicus: Tanzania coast dwarf galago, lowland forests at the coast of Tanzania, 104-172 g.
P. zanzibaricus zanziparicus, Zanzibar dwarf galago, Zanzibar island, individuals are smaller in the island
P. zanzibaricus udzunwensis, Matundu dwarf galago, several lowland forests of Tanzania, 118-195 g.
P. granti: Mozambique dwarf galago, southern Tanzania Malawi, Zimbabwe and Mosambique, 165 g.
P. orinus: Mountain dwarf galago, Udzungwa and Uluguru mountains Tanzania, 74-98 g. One of 25 most endangered primates of the world by IUCN and IPS.
P. rondoensis: Rondo dwarf galago, six fragmented patches of moist forest on the coast Tanzania, 60-73 g.
Nomenclature history of P. cocos, Kenya coast galago
Thomas Butynski and he’s colleagues reviewed compex taxonomy of dwarf galagos of East African species in 2006 (Butynski et al., 2006). At this time genus of Eastern dwarf galagos was still Galagoides. However, for clarity I will use here genus Paragalago.
Edmund Heller named the species in 1912, he considered it to be subspecies of Galago moholi. He collected 10 specimens from Mazeras, Kenya, from area of coconut palms and bushland, not from forest.
P. cocos was raised to species status by Elliot 1913, but for a long time it was considered to be subspecies of the Somali lesser galago (Galago gallarum cocos) or as subspecies of the Zanzibar galago (P. zanzibaricus).
Ecology, behavior and vocal repertoire of P. cocos was studied in the field thoroughly in Diani and Gedi Forests, Kenya (Harcourt & Nash, 1986a,b; Harcourt & Perkin, 2013). In Harcourt & Nash articles species was named as P. zanzibaricus, but research was beginning to show that species was not P. zanzibaricus but in fact P. cocos.
Diani and Gedi forests were 40 km from Mazeras where Heller collected P. cocos specimens in 1911. Thomas Butynski and Yvonne de Yong visited Mazeras in 2004 and confirmed that species there is P. cocos. It was the same species as in Diani and Gedi forests.
Reading former research nomenclature of the species may be confusing, as species is named as P. zanzibaricus in many papers before 2006 and sometimes research has been done on several species. However, since article by Butynski et al. 2006 P. cocos has had full consensus about its species status, this was mainly based on distinctively different advertising calls.
Geographic range of P. cocos
P. cocos occurs in evergreen forest all along the coastal strip of Kenya, south of the Tana River, southward to Mgambo Forest Reserve in northern Tanzania and to north end of East Usambara Mountains (Harcourt & Perkin, 2013). Altitudional range for P. cocos is 0-350.
P. cocos is the northern species, P. zanzibaricus is the central species and P. granti is the southern species. it is possible that P. cocos and P. zanzibaricus are parapatric at a few sites to the north of the East Usambara Mountains in the coastal strip of north-eastern Tanzania (Butynski et al. 2006].
Results of genetic studies in P. cocos and P. zanzibaricus
Molecular clock analyses estimated the divergence ages between P. cocos and P. zanzibaricus at approximately 3 Ma, in the Late Pliocene (Pozzi et al., 2020). This research confirmed that advertising calls can be correctly used for species identification.
In many nocturnal mammal’s species have different advertisement calls for species recognition, thus preventing hybridization of species. It is also possible that divergence in acoustic communication is result of isolation and genetic drift.
Reason for high species number in Paragalago
Biogeographical changes during last five million years lead to disappearance of large forests and formation of savannas in East Africa. This is also boosted human evolution. Remaining forests became isolated patches on the tops of the Eastern Arch Mountains and in the lowland coastal forests. Forests covering Eastern Arch Mountains are 30 million-year-old. It is natural that during long isolation species began to develop to different species due to adaptation to local environment and genetic drift.
Masters et al. (2017) stated that the Eastern Arch Mountains and the coastal forests of Kenya, Tanzania and Mosambique form a separate area, Zanj subregion. The Zang mammalian fauna is unique and deserves highest conservation priority. This is one of the biodiversity hotspot areas of the world.
Some of the key researchers of dwarf galagos
Simon Bearder, Thomas Butynski, Andrew Perkin, Yvonne de Yong, Magdalena Svensson, Caroline Harcourt, Leanne Nash, Paul Honess, Judith Masters, Anna Nekaris
Dwarf galago research is challenging for many reason. Animal is tiny, fast, sometimes very shy and nocturnal.
Bearder SK. 1999. Physical and social diversity among nocturnal primates: A new view based on long term research. Primates 40:267–282. DOI: 10.1007/BF02557715.
Butynski TM, de Jong YA, Perkin AW, Bearder SK, Honess PE. 2006. Taxonomy, Distribution, and Conservation Status of Three Species of Dwarf Galagos (Galagoides) in Eastern Africa. Primate Conservation 21:63–79. DOI: 10.1896/0898-6184.108.40.206.
Harcourt CS, Nash LT. 1986a. Social organization of Galagos in Kenyan coastal forests: I.Galago zanzibaricus. American Journal of Primatology 10:339–355. DOI: 10.1002/ajp.1350100406.
Harcourt CS, Nash LT. 1986b. Species differences in substrate use and diet between sympatric galagos in two Kenyan coastal forests. Primates 27:41–52. DOI: 10.1007/BF02382521.
Harcourt CS, Perkin AW. 2013. Galagoides cocos Kenya Coast Dwarf Galago (Diani Dwarf Galago). In: Mammals of Africa. Bloomsbury,.
Masters JC, Génin F, Couette S, Groves CP, Nash SD, Delpero M, Pozzi L. 2017. A new genus for the eastern dwarf galagos (Primates: Galagidae). Zoological Journal of the Linnean Society 181:229–241. DOI: 10.1093/zoolinnean/zlw028.
Pozzi L, Penna A, Bearder SK, Karlsson J, Perkin A, Disotell TR. 2020. Cryptic diversity and species boundaries within the Paragalago zanzibaricus species complex. Molecular Phylogenetics and Evolution 150:106887. DOI: 10.1016/j.ympev.2020.106887.
Rosti H, Rikkinen J, Pellikka P, Bearder S, Mwang’ombe J. 2020. Taita Mountain dwarf galago is extant in the Taita Hills of Kenya. Oryx 2020:151–153. DOI: https://doi.org/10.1017/S003060531900142X.
Svensson MS, Bersacola E, Mills MSL, Munds RA, Nijman V, Perkin A, Masters JC, Couette S, Nekaris KA-I, Bearder SK. 2017. A giant among dwarfs: a new species of galago (Primates: Galagidae) from Angola: Svensson et al. American Journal of Physical Anthropology 163:30–43. DOI: 10.1002/ajpa.23175.