Clinging to Survival: Critically Endangered Chapman's Pygmy Chameleon Rhampholeon Chapmanorum Persists in Shrinking Forest Patches
Total Page：16
File Type：pdf, Size：1020Kb
Clinging to survival: Critically Endangered Chapman's pygmy chameleon Rhampholeon chapmanorum persists in shrinking forest patches K RYSTAL A. TOLLEY,COLIN R. TILBURY,JESSICA M. DA S ILVA,GARY B ROWN Y ANKHO C HAPETA and C HRISTOPHER V. ANDERSON Abstract The Critically Endangered Chapman’spygmycha- Introduction meleon Rhampholeon chapmanorum is endemic to the low verall extinction risk for chameleons is substantially elevation rainforest of the Malawi Hills in southern Malawi. higher than the global average of c. % for squamate Much of this forest has been converted to agriculture and O reptiles (Böhm et al., ), with % of species categorized it was uncertain whether chameleon populations have per- as threatened and % as Near Threatened (IUCN, ). sisted. We used current and historical satellite imagery to Most threatened species are forest specialists, with habitat identify remaining forest patches and assess deforestation. loss and degradation being the primary threat (Tolley We then surveyed forest patches for the presence of this et al., ). Given that forest chameleons are intolerant of chameleon, and assessed its genetic diversity and structure. transformed habitats, as forest is lost chameleon popula- We estimated that % of the forest has been destroyed tions decline and become locally extinct. There are five since , although we found extant populations of the Critically Endangered forest-living chameleon species in chameleon in each of the patches surveyed. Differentiation mainland Africa, all threatened by forest loss (IUCN, of genetic structure was strong between populations, suggest- ). They inhabit small rainforest patches on mountain ing that gene flow has been impaired. Genetic diversity was inselbergs that tend to have high endemicity (Menegon not low, but this could be the result of a temporal lag as et al., ; Conradie et al., ; Gereau et al., ; well as lack of sensitivity in the mitochondrial marker used. Lyakurwa et al., ). Thus, the loss of forest patches results Overall, the impact of forest loss is assumed to have led to in the extinction of endemic species (e.g. Betts et al., ), a large demographic decline, with forest fragmentation including chameleons. preventing gene flow. The Critically Endangered Rhampholeon chapmanorum Keywords Africa, Chapman’s pygmy chameleon, extinc- is a small (.–. cm body length), terrestrial chameleon en- tion, habitat loss, Malawi, reptile, Rhampholeon chapmano- demic to the low elevation rainforest of the Malawi Hills rum, threatened species near Nsanje in southern Malawi (Fig. , Plate ). These mountains rise to c. m and were once covered by dense rainforest, primarily on the eastern slopes between – m (Dowsett-Lemaire et al., ). At the time of the description of R. champanorum there were indications that substantial areas of forest were being lost (Tilbury, ). To safeguard the species, individuals ( females and males) from the type locality in the Malawi Hills were released in in a forest patch at Mikundi, KRYSTAL A. TOLLEY* (Corresponding author, orcid.org/0000-0002-7778-1963) † and JESSICA M. DA SILVA ( orcid.org/0000-0001-8385-1166) South African Malawi, c. km to the north (Dowsett-Lemaire et al., National Biodiversity Institute, Kirstenbosch Research Centre, Private Bag X7 ; Tilbury, ). Follow-up surveys at the release site Claremont 7735, Cape Town, South Africa. E-mail [email protected] in and confirmed the population was present COLIN R. TILBURY Department of Botany & Zoology, University of Stellenbosch, (C.R. Tilbury, unpubl. data). However, given the apparent Stellenbosch, South Africa loss of forest in the species’ natural range, it was uncertain GARY BROWN Les Terrasses, Sainte Innocence, France whether the remaining forest fragments still contained vi- ‡ YANKHO CHAPETA Museums of Malawi, Chichiri, Blantyre, Malawi able populations (Tolley et al., ). CHRISTOPHER V. ANDERSON ( orcid.org/0000-0001-7411-3102) Department of Rhampholeon chapmanorum is unlikely to inhabit trans- Biology, University of South Dakota, Vermillion, USA formed areas, and therefore forest degradation, fragmen- *Also at: School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa tation and loss would be expected to cause an overall †Also at: Department of Zoology, Centre for Ecological Genomics & Wildlife demographic decline (e.g. Andrén, ), leading to local Conservation, University of Johannesburg, Johannesburg, South Africa extinctions. Furthermore, the loss of connectivity between ‡Also at: Biological Sciences Department, Mzuzu University, Luwinga, Mzuzu, Malawi populations affects ecosystem functioning, disrupts meta- Received February . Revision requested May . populations, reduces gene flow and increases genetic popu- Accepted September . lation structure even over small spatial scales. Thus, the This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, Downloadeddistribution, from https://www.cambridge.org/core and reproduction in any medium,. IP address: provided 170.106.35.234 the original work, on is 23 properly Sep 2021 cited. at 08:28:06, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/termsOryx, Page 1 of 6 © The Author(s),. https://doi.org/10.1017/S0030605320000952 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605320000952 2 K. A. Tolley et al. PLATE 1 Male Rhampholeon chapmanorum in Mabunga forest. historical satellite imagery as a proxy to gauge demographic decline, and examined the genetic structure and diversity of the populations. Because there are no historical baseline estimates of population size or genetic structure/diversity, we assume that demographic decline is proportional to for- est loss. We predicted that fragmentation has disrupted gene flow, leading to strong differentiation of genetic structure and low genetic diversity. Methods We estimated the extent of forest loss using historical (/ ) and recent () satellite imagery of Malawi Hills FIG. 1 (a) Overview map of sites searched for Rhampholeon chapmanorum. Broken circle shows the locality for Mikundi from Google Earth (Google, Mountain View, USA). His- (exact locality obscured) and the square shows the Malawi Hills torical satellite images were of poor quality, and therefore locality, and (b) forest patches in the Malawi Hills superimposed images from both and were used. Polygons were on a topographic map with contour lines. The present extent of created around each of the forest patches for these time per- forest patches is shaded, with the estimated extent in / iods, exported as kmz files, mapped in QGIS . (QGIS shown by the dotted lines. Type locality is indicated by the black Development Team, ) and their areas quantified. The dot. Forest patches are numbered as in Table , except patches m contour was used as a guide to assess where low and , which were not surveyed. elevation rainforest might have originally occurred (e.g. Dowsett-Lemaire et al., ). effect of habitat loss on the population is both direct (via Logistical constraints did not allow us to survey all the population decline) and indirect because genetic diversity forest patches, but we were able to access two forest patches and gene flow are expected to diminish over time, reducing in the Malawi Hills and one at Mikundi, during – March the adaptive potential of the population (Haddad et al., ; (Fig. ). We walked forest trails at night to record cha- Leigh et al., ). The latter effects can be amplified in small meleons, using torchlight. Transects were defined by pres- populations because genetic drift is greater, leading to strong ence of trails and were therefore neither randomly chosen differentiation in genetic structure between populations, nor of a set distance or time. The location of each chameleon and inbreeding depression through fixation of deleterious encountered was recorded (± m) and a tissue sample was alleles and elevated homozygosity, reducing resilience (Hanski, taken from a subset of adult chameleons (c. mm tail clip) ). Information on population size, spatial genetic struc- for genetic analysis. All individuals were returned to the ture and diversity is therefore required to understand fully same perch on which they were found. the extinction risk for R. chapmanorum. To assess the genetic diversity within and between popu- To investigate these issues, we surveyed forest patches lations from each forest patch, an bp fragment of the in both Malawi Hills and Mikundi, to assess whether ND mitochondrial gene was sequenced for individ- R. chapmanorum populations are extant, quantified the ex- uals. Genomic DNA was extracted using salt extraction tent of forest loss in the Malawi Hills using recent and (MacManes, ). ND was amplified in a PCR reaction Oryx, Page 2 of 6 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605320000952 Downloaded from https://www.cambridge.org/core. IP address: 170.106.35.234, on 23 Sep 2021 at 08:28:06, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0030605320000952 Chapman’s pygmy chameleon 3 TABLE 1 Forest patch areas in the Malawi Hills in / and , with estimated extent lost. Patch numbers (in parentheses) correspond to the numbers in Fig. b. Forest patch (no.)