Lizards used as bioindicators to monitor pesticide contamination in sub-Saharan Africa: A review

Michael R.K. Lambert1

Natural Resources Institute, University of Greenwich at Medway, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK 1Deceased. Correspondence to A. Hailey, Department of Life Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago, West Indies e-mail: [email protected]

Abstract. To monitor the environmental effects of pesticides, population and community metrics for lizards (e.g., species composition, relative density, percentage niche occupied) should be recorded before and after applications, or compared between treated and untreated areas, in parallel with samples collected for laboratory residue analysis. In monitoring studies focused on lizard habitat, numerically predominant lizard species may be identified from preliminary field surveys, and subsequently used as bioindicators. Lizards will be especially useful as bioindicators during dry seasons or in arid regions lacking amphibians. Characteristics of lizards making them suitable for use as bioindicators of pesticides and other environmental contaminants are reviewed.

Key words: Bioindicator; environmental contaminants; lizards; pesticides; sub-Saharan Africa.

Introduction Lizards are potentially useful bioindicators of pesticide contamination in terrestrial habitats since they are sensitive to pesticides, as noted by Hall (1980) nearly 25 years ago, and their residue loads may give an indication of pesticide levels entering food chains (Lambert, 1997a). Lizards are also relatively conspicuous in the field, and form an important faunal component in arid and semi-arid areas. They maintain activity during tropical dry seasons and are thus especially suitable for use as bioindicators in xeric habitats from which amphibians (also useful bioindicators) are absent. Few lizards or other reptiles, however, have been used for toxicity testing, and little information is therefore available on their general sensitivity to pesticides. The potential of lizards as bioindicators was proposed by Sharygin (1984) with special reference to heavy metals, and by Lambert (1987) for pesticide contamination. The characteristics specifically of lizards, in comparison with those

© Koninklijke Brill NV, Leiden, 2005 APPLIED HERPETOLOGY 2: 99-107 Also available online - www.brill.nl 100 Michael R.K. Lambert of amphibians which are already known to be good bioindicators of pesticides and other environmental contaminants (Dunson et al., 1992; Sparling, 2000), are here re- assessed since my previous review (Lambert, 1997a). In light of further data from elsewhere in the world, the information from sub-Saharan Africa was placed into perspective in reviews by both Portelli and Bishop (2000) and Pauli and Money (2000), who further stressed the shortage of available data. Additional research on the subject was proposed as a requirement in a still more comprehensive review by Campbell and Campbell (2000). Findings from previously published work for sub- Saharan Africa (Lambert, 1993, 1994, 1997b) have in this paper been integrated with additional supportive unpublished data from a field survey in Mauritania and Senegal (Lambert, 1996), since this represented an example of an assessment specifically undertaken to determine the potential of lizards as bioindicators of pesticide contamination on the continent of Africa. An outline of the main results was given earlier in a publication for general biologists (Lambert, 1999).

Selection of Lizard Species as Bioindicators Numerically predominant forms were recognised from determinations of species composition (percentage frequencies) in populations of lizards in different parts of sub-Saharan Africa. Lizards sighted in stands of mopane woodland exposed to insecticide treatment against tsetse flies in NW Zimbabwe (southern central Africa) provided information on species composition (Lambert, 1993). Species richness was indicated by the number of species recorded. In mopane woodland, the arboreal skink Mabuya striata wahlbergii had the highest percentage frequency (82.9% of samples in untreated areas) and was therefore selected as the main bioindicator species. In Somaliland, numerically predominant lizards were determined from a survey within the vicinity of heavy spillage from a destroyed pesticide store near Hargeisa in March/April 1993. Four species were selected for use as biomarkers of the levels of pesticide residues entering food chains (Lambert, 1997b). These were the loose rock- and rubble-dwelling Hemidactylus parkeri (Gekkonidae) and the fossorial Chalcides ragazzii (Scincidae), which were both abundant in the vicinity of the spill; the ground-dwelling Mabuya s. striata (Scincidae), which were in and around Hargeisa, by buildings and garden walls in the valley below the spill; and the surface-dwelling Pseuderemias smithi (Lacertidae). Lizards in Sahelian West Africa were sighted in habitats exposed to pesticide treatment against locusts and weaver birds. Species composition was determined in six habitats during September/October 1996 in Senegal and southern Mauritania, but only in four habitats were lizards recorded in sufficient numbers to be identified as bioindicators. Insufficient numbers were observed in either open sand dune (only a single Scincus albifasciatus was recorded at one of three sites in southern Mauri- tania) or wetland habitats (only 0, 2 or 3 individuals of the large monitor lizard, Varanus niloticus, were recorded at three sites). In the remaining four habitats,