Our Research

Research Overview

My research integrates the morphology and physiology of organisms with their ecology and evolution to understand consequences of hypoxic stress on fish and interactions of hypoxia with other environmental stressors (e.g., climate warming, invasive species). We focus on freshwater fishes in lakes, rivers, and swamps of East Africa, where we have long-term (30-year) field base at the Makerere University Biological Field Station in Kibale National Park, Uganda (https://bfs.mak.ac.ug/) and a satellite base at Lake Nabugabo. We also conduct research on Canadian fish species at risk, in particular imperiled cyprinid fishes. Information on past research and current projects is presented below.

Cyprinid fish from a swamp in Kibale National Park, Uganda
A small cyprinid fish from a swamp in Kibale National Park using Aquatic Surface Respiration (ASR), a widespread response to hypoxia in water-breathing fishes and the air-breathing African lungfish Protopterus aethiopicus.

Research: Past Efforts and Current Projects

Theme I: Effects of Environmental Stressors on Fishes

The ongoing loss of biodiversity in response to human transformations of the environment is a critical and compelling scientific issue. Hypoxia (low dissolved oxygen, DO) is a serious manifestation of anthropogenic stress to inland and coastal waters that can negatively affect performance and fitness-related traits in fishes. Climate change is likely to exacerbate impacts of hypoxia on fishes, because oxygen solubility in water decreases with rising temperature, while fish metabolism (rate of oxygen consumption) increases. Given that hypoxia and global warming are both pervasive aquatic stressors, there is a need to address their interactive effects, particularly in (a) tropical fishes that are predicted to be more sensitive to climate change and (b) endangered fishes with limited ranges that must respond in situ to environmental change. Our long-term studies of East African fishes in Uganda have demonstrated that dissolved oxygen (DO) is a strong predictor of intraspecific variation in morphology and physiology of fishes that affects performance, fitness traits, and ecological interactions. We have also found a strong element of development plasticity in response to long-term hypoxia exposure. Our recent studies of thermal tolerance have documented thermal acclimation capacity in multiple species of equatorial fishes and provided the first evidence for cardiac remodelling in a tropical fish, challenging predictions that tropical fish have limited thermal plasticity. We are now building on these foundational studies to explore interactive effects of hypoxia and thermal stress in both tropical and temperate fishes, as well as effects of other stressors that may affect oxygen uptake and delivery systems (e.g., water turbidity).

Past Research

Morpho-physiological Divergence across Oxygen Gradients -- An important step in studies of evolutionary diversification is to document patterns of variation between populations from contrasting environments. For fishes, the availability of dissolved oxygen (DO) in their environment can affect many traits across all levels of biological organization (e.g., molecular, physiological, morphological) and may therefore lead to divergence across habitats that differ DO. By comparing fish species that cross strong DO gradients (e.g., hypoxic swamps vs. well-oxygenated streams) in Uganda we have demonstrated that DO is a strong predictor of intraspecific variation, particularly in respiratory traits (e.g., gill size), as well as key life-history traits (fecundity, egg size), energetics, hormone levels, body shape, and brain size.

Dark, hypoxic water of a papyrus swamp in Uganda meets the turbid open river water
The dark hypoxic waters of the Rwembaita Swamp meet the high-oxygen waters of the Njuguta River in Kibale National Park, Uganda.

Selected publications:

Chapman, L.J. Low-oxygen lifestyles in extremophilic fishes. 2015. In: R. Reisch, M. Plath, M. Tobler (Editors) Extremophile Fishes - Ecology and Evolution of Teleosts in Extreme Environments. Springer, Heidelberg. Pp. 9-33.

Friesen, C.N., N. Aubin-Horth, and L.J. Chapman. 2012. The effect of hypoxia on sex hormones in an African cichlid Pseudocrenilabrus multicolor victoriae. Comparative Biochemistry and Physiology Part A 162:22-30. doi: 10.1016/j.cbpa.2012.01.019

Langerhans, R.B., L.J. Chapman, and T.J. DeWitt. 2007. Complex phenotype-environment associations revealed in an East African cyprinid. Journal of Evolutionary Biology 20:1171-1181.

Chapman, L.J. and K. Hulen. 2001. Implications of hypoxia for the brain size and gill surface area of mormyrid fishes. Journal of Zoology 254:461-472.

Chapman, L.J., C.A. Chapman, D. Brazeau, B. McGlaughlin, and M. Jordan. 1999. Papyrus swamps and faunal diversification: Geographical variation among populations of the African cyprinid Barbus neumayeri. Journal of Fish Biology 54:310-327.

Plastic Response to Hypoxia -- In a series of studies on the cichlid Pseudocrenilabrus multicolor) reared under low- and high-dissolved oxygen, we have provided evidence for a strong element of developmental plasticity in morpho-physiological traits (e.g., gill size) in response to oxygen availability, but also evidence of genetic components to diversity among populations (e.g., body shape, egg size), as well as interactions between population (genetic) and treatment (hypoxia) effects (e.g., brain mass). We have also used acclimation studies to quantify effects of short-term hypoxia exposure on a suite of behavioural, physiological, and sensory traits. For example, our studies of weakly electric mormyrid fishes demonstrated that hypoxia exposure affects sensory information acquisition, that periodic re-exposure to hypoxia can increase a fish’s ability to cope with future bouts of hypoxic stress, and that hypoxia tolerance is reduced in mormyrids acclimated to normoxia, suggesting high costs of hypoxia adaptation.

A brightly coloured male cichlid
Pseudocrenilabrus multicolor male, a widespread haplochromine cichlid that is found across broad environmental gradients including hypoxic swamps and well-oxygenated lakes and rivers.

Selected publications:

Clarke, S.B., L.J. Chapman, and R. Krahe. 2019. The effect of normoxia exposure on hypoxia tolerance and sensory sampling in swamp-living fish. Comparative Biochemistry and Physiology. 240:11058. doi/prg/10.1016/j.cbpa.2019.110586

Ackerly, K.L., R. Krahe, C.P. Sanford and L.J. Chapman. 2018. Effects of hypoxia on swimming and sensing in a weakly electric fish. Journal of Experimental Biology 221: doi: 10.1242/jeb.172130

Crispo, E. and L.J. Chapman. 2010. Geographic variation in phenotypic plasticity in response to dissolved oxygen in an African cichlid fish. Journal of Evolutionary Biology 23:2091-2103. doi: 10.1111/j.1420-0101.2010.02069.x

Wiens, K., E. Crispo, and L.J. Chapman. 2014. Phenotypic plasticity is maintained despite geographical isolation in an African cichlid fish, Pseudocrenilabrus multicolor. Integrative Zoology 9:85-96. doi: 10.1111/1749-4877.12029

Crocker, C.D., L.J. Chapman, and M.L. Martinez. 2013. Hypoxia-induced plasticity in the metabolic response of a widespread cichlid. Comparative Biochemistry and Physiology B166:141-147. doi: 10.1016/j.cbpb.2013.08.002

Reardon, E.E. and L.J. Chapman. 2010. Energetics of hypoxia in a mouth-brooding cichlid: Evidence for interdemic and developmental effects. Physiological and Biochemical Zoology 8:414-423. doi: 10.1086/651100

Chapman, L.J., F. Galis, and J. Shinn. 2000. Phenotypic plasticity and the possible role of genetic assimilation: Hypoxia-induced trade-offs in the morphological traits of an African cichlid. Ecology Letters 3:388-393.

Hot Fish in a Warming World -- Tropical fishes may more sensitive to climate warming than temperate species because they experience small annual temperature fluctuations and seem to live close to their maximum thermal tolerance. We have made significant advances in understanding effects of warming waters on equatorial fishes. Using a trait-based vulnerability assessment, we showed that nearly 40% of African fishes are highly vulnerable to climate change. Interestingly, our studies of thermal tolerance revealed that several species of equatorial fishes show acclimation capacity in the upper thermal limits. For Nile perch, we demonstrated that aerobic scope can be maximal at temperatures near the limit of ecological relevance. Together, these results challenge predictions that tropical fishes have limited thermal plasticity, and that high temperatures will be detrimental due to limitations in aerobic scope. We have also provided new insights on deforestation-induced warming. We demonstrated that forest conversion strongly influences several biotic steam temperature and invertebrate communities, but that fish may offset metabolic costs of deforestation-induce warming with increased consumption.

Outdoor tanks at the Aquaculture Research & Development Center in Uganda
Outdoor facilities at the Aquaculture Research & Development Center in Kajjansi, Uganda for rearing juvenile Nile perch under different water temperatures.

Selected publications:

Nyboer, E., C. Liang, and L.J. Chapman. 2019. Assessing the vulnerability of Africa’s freshwater fishes to climate change: a continent-wide trait-based analysis. Biological Conservation 236:505-520. doi.org/10.1016/j.biocon.2019.05.003

Lapointe, D, M. Cooperman, L. Chapman, T. Clark, A. Val, M. Ferreira, J. Balirwa, M. Dismas. M Matthew, L Chhom, L. Hanna, L. Kaufman, A. Farrell, and S. Cooke. 2018. Predicted impacts of climate warming on aerobic performance and upper thermal tolerance of six tropical freshwater fishes spanning three continents. Conservation Physiology 6(1): coy056 doi:10.1093/conphys/coy05

Nyboer, E.A. and L.J. Chapman. 2018. Cardiac plasticity influences aerobic performance and thermal tolerance in a tropical, freshwater fish at elevated temperatures. Journal of Experimental Biology 221 doi: 10.1242/jeb.178087

Fugère, V., Mehner, T. and L.J. Chapman. 2018. Impacts of deforestation-induced warming on the growth and trophic interactions of a stream fish: assessing the relative importance of metabolic effects in a multiple stressors context. Functional Ecology 32:1343-1357. doi: 10.1111/1365-2435.13065

Nyboer, E.A. and L.J. Chapman. 2017. Elevated temperature and acclimation time affect metabolic performance and growth in the heavily exploited Nile perch of Lake Victoria. Journal of Experimental Biology 220:3782-3793 doi: 10.1242/jeb.163022

McDonnell, L.H. and L.J. Chapman. 2015. At the edge of the thermal window: Effects of elevated temperature on the resting metabolism, hypoxia tolerance, and upper critical thermal limit of a widespread African cichlid. Conservation Physiology 3. doi: 10.1093/conphys/cov050

Current Projects

Independent and Interactive Effects of Hypoxia and Climate Warming – We are using a combination of field eco-physiology assays, field survey, and laboratory rearing studies to explore interactive effects of hypoxia and climate warming on fish performance and fitness in two phylogenetically distant families of fishes from Uganda. Field survey and experiments at field stations in Uganda allow us to quantify variation in thermal windows, thermal- and hypoxia tolerance, aerobic performance, and fitness-related traits among fish populations from different temperature and DO regimes. Common-garden lab studies on fish live transferred to McGill are used to experimentally quantify interactive effects of life-long exposure to hypoxia and warming on performance and fitness-related traits. Together, these studies will test the prediction that adaptations to hypoxia may help fish to cope with climate warming and address a key question in thermal biology of ectotherms – whether thermal tolerance is limited by aerobic capacity.

The Chapman lab in wetlands of Uganda.
Field sampling at research sites in Uganda.

Interactions between Local Adaptation & Range Expansion in the Face of Climate Warming -- Tolerance to rapid environmental change varies among species and has the potential to rapidly evolve. In addition, if organisms are adapted to divergent environmental conditions within their range, the ability to track or adapt to changing environments may differ between locally adapted ecotypes. The recent range expansion of native fish species that we have documented from lower reaches of two Ugandan rivers into low- and high-DO upstream reaches provides an excellent opportunity to examine how locally-adapted ecotypes (fish from low-DO and high-DO habitats) differ in their ability to track environmental change. In collaboration with Hendry/Barrett labs (Redpath Museum, McGill University), we are integrating 30 years of baseline data with field distributional studies, ecophysiological assays (hypoxia and thermal tolerance), phenotyping (morphology, shape, respiratory traits), and genomics to understand and predict range expansion of native fish species within and across ecotypes and to explore the degree to which colonization of new divergent habitats is parallel from a phenotypic and genetic basis.

Two native species of fishes in Uganda.
Two native species (left: Enteromius neumayeri and right: Hypsopanchax deprimozi) that have expanded their range to the north in the Mpanga River drainage of Kibale National Park, Uganda.

Deforestation-Induced Warming -- Our recent studies in Ugandan streams have demonstrated that forest conversion strongly influences abiotic and biotic variables, with a greater maximum temperature and greater fluctuations in deforested streams. In a lab thermal acclimation experiment on the African cyprinid Enteriomius neumayeri from forested and deforested streams, warming increased metabolic rates and decreased growth, but we found no evidence of local (thermal) adaptation. We are now building on this set of studies to explore effects of constant vs. fluctuating diel regimes of temperature on traits related to oxygen supply capacity and thermal tolerance across multiple exposure domains (acclimation, life-long). We will blend field surveys, acclimation experiments, and rearing studies on populations of fish from deforested and forested streams.

A forested and deforested stream inside Kibale National Park, Uganda
A forested stream inside Kibale National Park and a deforested stream outside the park, where we are conducting studies on the phenotypic divergence and energetics of Enteromius neumayeri.

Effects of Multiple Stressors on Canadian Fish Species at Risk -- The Lower Great Lakes watershed of Canada has 32 fish and 15 mussel species at risk (SAR) that are found in variety of habitats including small headwater streams, large rivers, wetlands, and lakes. Major threats include habitat degradation and loss that exposes fish to multiple stressors including increased water turbidity and hypoxia. Climate change is an emerging threat that may compound effects of other anthropogenic stressors on these already vulnerable species at risk. As part of the Canada Freshwater Species at Risk Research Network (SAR NET) and in collaboration with Dr. Nicholas Mandrak (UT Scarborough), we are evaluating the independent and interactive effects of environmental stressors (hypoxia on performance, tolerance, and fitness-related traits of fish species at risk. These include the cyprinids Pugnose Shiner (Notropus anogenus, listed as Threatened under Canada’s Species at Risk Act (SARA), Redside dace (Clinostomus elongatus, listed as Endangered, SARA) and the catostomid Lake Chubsucker (Erimyzon sucetta, listed as Endangered, SARA). In a series of acclimation studies (both short-term and long-term), we found that Pugnose Shiner shows plasticity in several traits in response to long-term exposure to elevated water temperature that may facilitate persistence in warmer waters. However, acute hypoxia exposure reduced thermal tolerance, stressing the importance of evaluating interactive effects of multiple stressors. We have also found that Pugnose Shiner are more sensitive to turbidity than closely related shiners, stressing the need for species-specific studies in evaluating stressor thresholds. Our current research focuses on the independent and interactive effects of turbidity, hypoxia, and water temperature on Pugnose Shiner using a blend of laboratory acclimation studies, lake-side experiments, and habitat occupancy studies in the field.

Chapman lab: photos combining laboratory experiment sand field surveys
Lab and field research looking at effects of multiple stressors on the Threatened Pugnose Shiner (Notropis anogenus).

Selected Publications:

Gray, S.M., N. Mandrak, and L.J. Chapman. 2016. Species-specific effects of turbidity on the physiology of imperiled blackline shiners (Notropis spp.) in the Laurentian Great Lakes. Endangered Species Research 31:271-277. doi: 10.3354/esr00774

Gray, S.M., F.M.E. Bieber, L.H. McDonnell, L.J. Chapman, and N.E. Mandrak. 2014. Experimental evidence for species-specific response to turbidity in imperiled fishes. Aquatic Conservation doi:10.1002/aqc.2436

Theme II: Hypoxic Refugia and Biodiversity Conservation in the Lake Victoria Basin

Past Research

Hypoxia as a Modulator of Predator-Prey Interactions -- We have applied our understanding of respiratory ecology to conservation issues, in particular the role of hypoxic waters as refugia for endangered fishes in the Lake Victoria basin (East Africa), where many native fishes (particularly endemic haplochromine cichlids) disappeared coincident with the upsurge of introduced predatory Nile perch (Lates niloticus). In a series of studies on Lake Nabugabo, a satellite lake of Lake Victoria, we identified faunal refugia (e.g., hypoxic wetlands), examined characters that permit use of these habitats (traits related to hypoxia tolerance), and quantified cascading effects of fishing pressure on predator-prey dynamics. These studies have highlighted the importance of physiological refugia in modulating impacts of introduced predators. A second theme of our research in Lake Victoria basin has been to explore patterns of phenotypic change in fish species in response to the dynamic ecological changes in the basin. For example, we detected changes in life-history traits of Nile perch and the native cyprinid Rastrineobola argentea consistent with theoretical expectations for fisheries-induced selection.

Species of colourful male haplochromine cichlids (Lake Nabugabo, Uganda)
Species of haplochromine cichlids from Lake Nabugabo, Uganda.

Selected publications:

Chapman, L.J. and Sharpe, D.M.T. 2016. Harvest-induced phenotypic change in inland fisheries. In. J. Craig (Editor). The Ecology of Freshwater Fisheries, Wiley-Blackwell, Pp 626-640.

Sharpe, D., S.B. Wandera, and L.J. Chapman. 2012. Life history change in response to fishing and an introduced predator in the East African cyprinid Rastrineobola argentea. Evolutionary Applications 5:677-93. doi: 10.1111/j.1752-4571.2012.00245.x

Chapman, L.J. and D. McKenzie. 2009. Behavioural responses and ecological consequences. 2009. Pp. 26-77. In: Richards, J.G., A.P. Farrell, and C.J. Brauner (editors). Hypoxia in Fishes. Elsevier, San Diego.

Balirwa, J.S., C.A. Chapman, L.J. Chapman, I.G. Cowx, K. Geheb, L. Kaufman, R.H. Lowe-McConnell, O. Seehausen, J.H. Wanink, R.L. Welcomme, and F. Witte. 2003. Biodiversity and fishery sustainability in the Lake Victoria Basin: An unexpected marriage? Bioscience 53:703-715. Order of authorship alphabetical.

Chapman, L.J., C.A. Chapman, J.P. Olowo, P.J. Schofield, L.S. Kaufman, O. Seehausen, and R. Ogutu-Ohwayo. 2003. Fish faunal resurgence in Lake Nabugabo, East Africa. Conservation Biology 17:500-511.

Chapman, L.J., C.A. Chapman, F.G. Nordlie, and A.E. Rosenberger. 2002. Physiological refugia: Swamps, hypoxia tolerance, and maintenance of fish biodiversity in the Lake Victoria Region. Comparative Biochemistry and Physiology 133 (A):421-437.

Current Research

Predator-Prey Dynamics in Lake Nabugabo -- The Nile perch populations (abundance, size, life-history traits) in the Lake Victoria basin continue to change, and there is likely to be strong cascading effects of fisher-Nile perch interactions on native fish communities. To understand these changes and to predict response of the Nile perch and native species to multiple stressors, we are continuing to document long-term changes in the environment, fish communities, fish stocks, and fish phenotypes. We are also applying bioenergetics modelling to understanding cascading effects of fishing pressure on the Nile perch consumption of native fishes. And, we are building on our studies of the small cyprinid R. argentea to understand how increasing fishing pressure is affecting their abundance and life-history traits (collaboration with Dr. Diana Sharpe, Worcester State University). Our long-term data will also form the basis of new studies on effects of climate change on fish communities and performance and fitness-related traits of both native and introduced species. This research is being carried out in collaboration with the National Fisheries Resources Research Institute of Uganda (http://www.firi.go.ug/).

Chapman lab studies effects of fishing pressure on fish species in Uganda
Upper left to right: Nile perch (Lates niloticus, large and medium size captured by fishers) and mukene (Rastrineobola argentea); lower left to right: fish landing at Lake Nabugabo, fisher on Lake Nabugabo, mukene catch).

Theme III: Small Fish and Food Security in the Lake Victoria basin.

Project Title - Nutrifish: Harnessing dietary nutrients of under-utilized fish and fish processing by-products to reduce micronutrient deficiencies among vulnerable groups in Uganda -- This current project is an interdisciplinary effort funded by the IDRC CultAF Program and led by Dr. Jackson Efitre (Makerere University, Uganda) in collaboration with the National Fisheries Resources Research Institute of Uganda (Dr. Winnie Nkalubo, Director), Nutreal (U) Ltd. (Dr. Dorothy Nakimbugwe), and McGill University (Prof. L Chapman and Prof. Hugo Ramiro Melgar-Quiñonez, McGill Institute for Global Food Security). Micronutrient deficiencies are widespread in Uganda, particularly among vulnerable groups (women of reproductive age and children <5 years), in rural and urban poor communities. Fish provide not only an excellent source of protein, but also provide a rich source of bioavailable micronutrients. However, In Uganda, fish has become less available due to declining stocks of large fishes (>20 cm total length), as well as increased demand for exported fish, in particular the Nile perch. In response to decreasing catch of large-bodied fishes, fisheries have developed strategies for targeting small-bodied pelagic species (<20 cm total length). These include Engraulicypris bredoi (muziri), Brycinus nurse (ragoogi) and Rastrineobola argentea (mukene). The goal of the Nutrifish project is to increase availability (via stock assessment and development of sustainable management practices), accessibility, nutritional quality and consumption of under-utilized small fishes and processing by-products. As part of this larger program, our lab is quantifying the micronutrient composition of R. argentea, B. nurse, and E. bredoi and Nile perch carcasses, as well as the role of scales as a calcium reservoir. 



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