Potential sub-lethal effects of anticoagulant rodenticide exposure on coyotes in southern California – Ariana McKenzie (CSUF; advisor Dr. Paul Stapp)

A brown lizard on a white surfaceDescription automatically generated with medium confidence

Anticoagulant rodenticides are baited poisons used to control rodent infestations which target pathways responsible for the production of blood clotting proteins. There are two versions of ARs which have similar mechanisms but different toxicities: first generations (FGAR) require multiple feeding events to generate a lethal dose, whereas second generations (SGAR) only require one feeding event. Despite application restrictions, there is still a large issue of accidental poisoning of non-target wildlife. These animals may die from rodenticide poisoning, but there may also be subtle, sub-lethal effects, including poorer body condition and increased susceptibility to pathogens and parasites. Coyotes (Canis latrans), which are common medium-sized carnivores in urban and suburban areas of southern California, are exposed to rodenticides; however, little is known about the potential for sub-lethal effects.

I predicted that a significant proportion of coyotes would be exposed to at least one rodenticide, and I also expected exposure to anticoagulant rodenticides (ARs) would be associated with poorer body condition. I estimated AR exposure for 353 coyotes from southern California using a liver assay and collected various measures of body condition for a subset sample of 50 coyotes. Five different measure of condition were collected: body condition score (BCS), kidney fat index (KFI), mandible-based residual size (RSI-m), femur-based residual size (RSI-f), and helminth loads (HELM).

Nearly 98% of the 353 coyotes I sampled were found to have with at least one anticoagulant rodenticide exposure. SGARs, including bromadiolone, brodifacoum, and difethialone, were found in 97% of coyotes. FGARs were also detected in 75% of coyotes, but this was largely due to the presence of diphacinone. I used a principal components analysis to combine 4 body condition measures (KFI, RSI-m, RSI-f, and HELM), which explained 71.5% of the variation seen in the 50 coyotes sampled through PC1 (46.3%) and PC2 (28.2%). PC1 was seen as a measure of size and parasite loads, whereas PC2 was primarily a measure of kidney fat index and had a positive relationship with body condition score.

There may also be a relationship between body condition and age, with younger coyotes in poorer body condition compared to older coyotes. Coyotes are often born with helminths, such as roundworms, because of placental transmission, and high parasite loads can lead to severe anemia and weight loss. Thus, younger coyotes tended to be smaller, have higher parasite loads, and a lower body condition score. Healthier conditions in older coyotes may also result from their ability to exclude younger coyotes and reflect access to better resources. I am currently analyzing the relationship between body condition and ARs, but so far, I have seen that coyotes in southern California are highly exposed to anticoagulant rodenticides. The recent California ban on SGARs may help reduce this high exposure, but a large number of coyotes are still exposed to FGARs and these compounds might still contribute to sublethal effects.

The California horn snail, Cerithideopsis californica, is resistant to infection by swimming miracidia – Dan Metz (UCSD; advisor Ryan Hechinger)

A brown lizard on a white surfaceDescription automatically generated with medium confidence

Like the famous “social” insects, larvae of some trematodes (parasitic flatworms) form a colony with division of labor inside the first intermediate mollusk host1–6. In these colonies, small, specialized “soldier” worms aggressively attack any other trematode that attempts to infect the host (Fig. 1). Establishing experimental colonies would allow me to test mathematical models explaining the development of specialized castes in these social worms. Trematodes are parasites with complex, multiple-host life cycles that typically involve at least a mollusk first host and a vertebrate final host. To maintain the life cycle in the lab, each host must be infected in sequence. Several social trematode species infecting Cerithideopsis californica (the California horn snail) have been cultivated in lab-reared final hosts7–10. However, no records exist of experimental infection of the snail, C. californica.

Following existing protocols, I infected lab-reared chickens with three echinostomoid trematode species – Acanthoparyphium sp. (Fig. 2A), Cloacitrema sp. (Fig. 2B), and Parorchis sp. – and obtained adult worms with apparently viable eggs (Fig. 3). Using protocols modified from experiments in different snail-trematode systems11-15, I hatched miracidia (a swimming, host-seeking larval stage) from these eggs and attempted to infect naïve C. californica. I exposed 49 snails to Acanthoparyphium, 232 snails to Cloacitrema, and 92 to Parorchis. All miracidia were active, quickly found their target, and appeared to attach to and penetrate the foot or tentacles of the exposed snail. I was not, however, able to establish, or detect, any experimental infections in C. californica.

There are two likely explanations. First, infection success rates in the wild may be low. While there are data on prevalence and incidence for the trematodes of C. californica 16–19, no work has been published regarding the number of infective eggs or miracidia entering the environment per unit time. It may be the case that these snails in the wild are subjected to a constant “rain” of trematode larvae, the vast majority of which are defended against. A second possibility is that the trematode larvae produced from experimentally infected chickens had developmental deficiencies. This could arise through methodological errors or from differences in the immune system or physiology of lab-reared chickens versus the natural hosts of these worms.

Whatever the cause, C. californica has proven resistant to experimental infection by echinostomoid trematodes reared in lab-raised chickens. This work highlights the need for research into the epidemiology and physiology of trematode infection in the C. californica guild. Being able to establish experimental infections in the host snail is a much-needed tool for exploring the developmental biology of social trematodes.

A brown lizard on a white surface

Description automatically generated with medium confidence


Figure 1. Three Himasthla sp. B soldiers attacking a redia of Euhaplorchis californiensis. The “victim” of the attack is stained with neutral red to facilitate visualization. The gut of each soldier is filled with tissue from the victim. The pharynx of the bottom worm is engaged and actively sucking material from the victim.





A brown lizard on a white surfaceDescription automatically generated with medium confidence


Figure 2. Adult trematodes obtained from experimental infections. A. Acanthoparyphium sp. Eggs are visible as dark ovals (arrow) between the ventral sucker and the dark testis. B. Cloacitrema sp. These individuals were not fully mature and did not have viable eggs.





A brown lizard on a white surfaceDescription automatically generated with medium confidence



Figure 3. Developing Acanthoparyphium sp. eggs. A. Egg at 2 days post-collection. B. Egg at 16 days post-collection. A prominent eyespot (dark area) and epidermal plates are visible in the developing miracidium.




Literature cited

1. Hechinger, R. F., Wood, A. C. & Kuris, A. M. Social organization in a flatworm: trematode parasites form soldier and reproductive castes. Proc. R. Soc. B Biol. Sci. 278, 656–665 (2011).

2. Garcia-Vedrenne, A. E. et al. Social organization in parasitic flatworms - four additional echinostomoid trematodes have a soldier caste and one does not. J. Parasitol. 102, 11–20 (2015).

3. Garcia-Vedrenne, A. E. et al. Trematodes with a reproductive division of labour: heterophyids also have a soldier caste and early infections reveal how colonies become structured. Int. J. Parasitol. 47, 41–50 (2017).

4. Miura, O. Social organization and caste formation in three additional parasitic flatworm species. Mar. Ecol. Prog. Ser. 465, 119–127 (2012).

5. Leung, T. L. F. & Poulin, R. Small worms, big appetites: Ratios of different functional morphs in relation to interspecific competition in trematode parasites. Int. J. Parasitol. 41, 1063–1068 (2011).

6. Nielsen, S. S., Johansen, M. & Mouritsen, K. N. Caste formation in larval Himasthla elongata (Trematoda) infecting common periwinkles Littorina littorea. J. Mar. Biol. Assoc. United Kingdom 94, 917–923 (2014).

7. Fried, B. Infectivity, growth, and development of Parorchis acanthus (Trematoda) in the domestic chick. J. Parasitol. 59, 743–744 (1973).

8. LeFlore, W. B., Bass, H. S. & Martin, W. E. The life cycle of Cloacitrema michiganensis McIntosh, 1938 (Trematoda: Philophthalmidae). J. Parasitol. 71, 28–32 (1985).

9. Martin, W. E. & Adams, J. E. Life cycle of Acanthoparyphium spinulosum Johnston, 1917 (Echinostomatidae: Trematoda). J. Parasitol. 47, 777 (1961).

10. Adams, J. E. & Martin, W. E. Life cycle of Himasthla rhigedana Dietz, 1909 (Trematoda: Echinostomatidae). Trans. Am. Microsc. Soc. 82, 1 (1963).

11. T. Díaz, M., Hernández, L. E. & Bashirullah, A. K. Experimental life cycle of Philophthalmus gralli (Trematoda: Philophthalmidae) in Venezuela. Revista de Biología Tropical 50, 629–641 (2002).

12. Zischke, J. A. Redial populations of Echinostoma revolutum developing in snails of different sizes. J. Parasitol. 53, 1200–1204 (1967).

13. Kendall, S. B. Nutritional factors affecting the rate of development of Fasciola hepatica in Limnaea truncatula. J. Helminthol. 23, 179–190 (1949).

14. Dinnik, J. A. & Dinnik, N. N. Observations on the succession of redial generations of Fasciola gigantica Cobbold in a snail host. Z. Tropenmed. Parasitol. 7, 397–419 (1956).

15. Lim, H. K. & Lie, K. J. The redial population of Paryphostomum segregatum (Trematoda: Echinostomatidae) in the snail Biomphalaria glabrata. Zeitschrift für Parasitenkd. 32, 112–119 (1969).

16. Sousa, W. P. Interspecific antagonism and species coexistence in a diverse guild of larval trematode parasites. Ecol. Monogr. 63, 103–128 (1993).

17. Buck, J. C. et al. Host density increases parasite recruitment but decreases host risk in a snail–trematode system. Ecology 98, 2029–2038 (2017).

18. Resetarits, E. J., Torchin, M. E. & Hechinger, R. F. Social trematode parasites increase standing army size in areas of greater invasion threat. Biol. Lett. 16, 20190765 (2020).

19. Hechinger, R. F. & Lafferty, K. D. Host diversity begets parasite diversity: Bird final hosts and trematodes in snail intermediate hosts. Proc. R. Soc. B Biol. Sci. 272, 1059–1066 (2005).

The influence of environmental and social factors on aggregation behavior of the leopard shark along the southern California Coast - Jack H. May III (CSULB; advisor Dr. Chris Lowe

A brown lizard on a white surfaceDescription automatically generated with medium confidence

Mature female leopard sharks (Triakis semifasciata) aggregate in warm shallow water in summer months to raise their core body temperatures for physiological benefits, and potentially decrease gestation time (Hight & Lowe, 2007; Jirik & Lowe, 2012). Previous research has shown that warmer temperatures can decrease gestation times significantly in both dogfish (Scyhinus caniculalior) and Atlantic stingray (Dasyatis Sabina) (Harris, 1952; Snelson, Williams-Hooper, & Schmid, 1988; Wallman & Bennett, 2006). What we still do not know is whether abiotic and/or biotic conditions induce aggregating behaviors in leopard sharks. My objective is to determine to what degree environmental conditions and social needs may drive aggregation behavior.

Leopard sharks are an especially vulnerable species due to their life history, nearshore distribution, aggregating behavior, and even more so by the fact that the females sexually segregate. In fact, nearshore aggregating pregnant females can be removed en masse, thereby damaging the species’ ability to replenish itself (Mucientes et al., 2009; Nosal et al., 2014). Historically, nearshore fisheries efforts removed an unsustainable number of leopard shark individuals in the 1980’s and early 1990’s (Pondella & Allen, 2008). Leopard sharks are also slow to mature and have relatively small numbers of offspring, making them extremely susceptible to fishing and negative human interaction (Ebert, 2003; Kusher et al., 1992; Pondella & Allen, 2008).

For this project I operated an unmanned aerial vehicle (UAV) to fly over leopard shark aggregations at Santa Catalina Island to collect aerial georeferenced and time referenced footage. Over 150 aerial surveys were flown on 87 separate days during the summer of 2018 and 2019, resulting in 55 hours of video footage (Fig. 1). Temperature data loggers (HOBO 8K Pendant, Onset) were installed in a semi-grid at known aggregation sites to collect water temperature data from the seafloor. Temperature maps were created by interpolating water temperatures measured across the distribution of temperature loggers. The positions of sharks recorded from georeferenced aerial footage will be layered over the thermal maps to determine whether sharks are using the predicted thermal envelope.

Preliminary analysis shows that the leopard sharks within these aggregations are not exclusively occupying portions of the seafloor where highest temperatures were recorded. Sharks were also observed swimming in dense aggregations in a small area within the study site when temperature distribution was relatively uniform. This suggests that their preferred thermal environment may not be as limited as previously thought, when aggregating for social and defensive purposes. Understanding the temperature regime of leopard sharks aggregations is increasingly important, given the global shift in temperature distributions in our oceans. Estimating future suitable habitats will enhance our ability to spatially manage and protect this species. Ecological research utilizing drones to collect data is a relatively new approach and methods utilized in this study could be applicable for others conducting similar research.

A brown lizard on a white surfaceDescription automatically generated with medium confidence










Figure 1. (Left) Georeferenced aerial image of leopard shark aggregation from Catalina Harbor, Santa Catalina Island, CA. (Right) Location of sharks overlaid on interpolated thermal map of study site using ArcMap.

Literature Cited:

Ebert, D. (2003). Sharks, rays and chimaeras of California. Berkeley, California: University of California Press. 145 p.

Harris, J. (1952). A note on the breeding season, sex ratio and embryonic development of the dogfish Scyliorhinus canicula (L.). Journal of the Marine Biology Association of the United Kingdom. 31(2), 269–275.

Hight, B., & Lowe, C. (2007). Elevated body temperatures of adult female leopard sharks, Triakis semifasciata, while aggregating in shallow nearshore embayments: Evidence for behavioral thermoregulation? Journal of Experimental Marine Biology and Ecology. 352(1), 114–128.

Jirik, K., & Lowe, C. (2012). An elasmobranch maternity ward: Female round stingrays Urobatis halleri use warm, restored estuarine habitat during gestation. Journal of Fish Biology. 80(5), 1227-1245.

Kusher, D., Smith, S., & Cailliet, G. (1992). Validated age and growth of the leopard shark, Triakis semifasciata, with comments on reproduction. Environmental Biology of Fishes. 35(2), 187–203.

Mucientes, G., Queiroz, N., Sousa, L., Tarroso, P., & Sims, D. (2009). Sexual segregation of pelagic sharks and the potential threat from fisheries. Biology Letter. 5, 156–159.

Nosal, A., Caillat, A., Kisfaludy, E., Royer, M., & Wegner, N. (2014). Aggregation behavior and seasonal philopatry in male and female leopard sharks, Triakis semifasciata, along the open coast of southern California, USA. Marine Ecology Progress Series 499, 157–175.

Pondella, D., Allen, L. (2008). The decline and recovery of four predatory fishes from the Southern California Bight. Marine Biology. 154(2), 307–313.

Snelson, F., Williams-Hooper, S., & Schmid, T. (1988). Reproduction and ecology of the Atlantic Stingray, Dasyatis sabina, in Florida coastal lagoons. Copeia. 3(3), 729–739.

Wallman, H., & Bennett, W. (2006). Effects of parturition and feeding on thermal preference of Atlantic stingray, Dasyatis sabina (Lesueur). Environmental Biology of Fishes. 75(3), 259-267.

Effects of microplastic exposure on the growth and survival of larval California grunion - James Chhor (CSULB; advisor Dr. Darren Johnson)

James Chhor picture

Microplastics in our oceans can negatively affect fishes through both physical and chemical pathways. To better understand how fishes are affected by microplastics, I separately investigated physical and chemical routes of exposure using the larvae of California grunion (Leuresthes tenuis). Physical pathways typically entail the consumption of microplastics that can lead to acute gastrointestinal damage (Lu et al., 2016) or increased larval mortality (Mazurais et al., 2015). Chemical pathways instead involve the transfer of chemical pollutants, collectively referred to as leachates, which may impair early life development (Hermabessiere et al., 2017).

To make matters more complicated, microplastics may originate from virgin or exposed sources. Virgin microplastics are minimally processed (e.g., beads, nurdles, or pellets) while exposed microplastics are plastics that have been left in the environment for some time and may have absorbed, and thus concentrated, pollutants from the water. In fact, leachates from exposed sources often contain other persistent organic pollutants (Rochman et al., 2014). The distinction is important because virgin microplastics may be more benign compared to exposed microplastics. Exposed microplastics can also form a film, which makes them more likely to be ingested (Alimba and Faggio, 2019).

For my project, I exposed newly hatched grunion larvae to 9 different treatments that represented distinct aspects of microplastic pollution. Treatments were divided into 3 aspects: 1) microplastics versus leachates exposure, 2) virgin versus exposed sources, and 3) low or high concentration (Fig. 1). The final treatment was a control, with no exposure. During the experiments, I measured survival, growth rates, and feeding rates of the grunion larvae.

None of the experimental treatments significantly affected survival or feeding rates of larval grunion. By contrast, however, exposure to microplastic particles significantly reduced larval growth rates. Within the microplastic treatment group, both sources of the microplastics (virgin and exposed) appeared to cause this reduction. Since exposure to leachates did not significantly affect growth rates, we can conclude that a physical route of exposure had the largest effect on larval grunion and that ingestion of microplastics has negative consequences for growth.

Grunion are an iconic fish in California. The recreational fishery they form and spectacle of spawning on sandy beaches draws several thousands of people to the beaches each year. More importantly, grunion are also a key indicator species for the general health of Marine Protected Areas in Southern and Central California (California, 2018). However, the strength of grunion runs has been weakening in recent decades (Martin et al., 2019). Reasons for this long-term decline are not fully understood, but increases in microplastic pollution could be a factor. Narrowing down the mechanism of microplastic influence on growth, whether by tissue damage or some sort of interference with digestion, will be the next important step in this research.

James Chhor picture














Figure 1: Experimental design, depicting 9 treatments: (1) control, (2) low concentration of exposed microplastics, (3) low concentration of virgin microplastics, (4) high concentration of exposed microplastics, (5) high concentration of virgin microplastics, (6) leachate from a low concentration of exposed microplastics, (7) leachate from a low concentration of virgin microplastics, (8) leachate from a high concentration of exposed microplastics, and (9) leachate from a high concentration of virgin microplastics

James Chhor picture
Figure 2: Grunion larvae 1 week post hatch. Some microplastic particles are visible on the water surface

Literature Cited

Alimba, C.G., Faggio, C., 2019. Microplastics in the marine environment: Current trends in environmental pollution and mechanisms of toxicological profile. Environmental Toxicology and Pharmacology 68, 61-74.

California, S.o., 2018. Coastal Regional Sediment Management Plans.

Hermabessiere, L., Dehaut, A., Paul-Pont, I., Lacroix, C., Jezequel, R., Soudant, P., Duflos, G., 2017. Occurrence and effects of plastic additives on marine environments and organisms: A review. Chemosphere 182, 781-793.

Lu, Y., Zhang, Y., Deng, Y., Jiang, W., Zhao, Y., Geng, J., Ding, L., Ren, H., 2016. Uptake and accumulation of polystyrene microplastics in zebrafish (Danio rerio) and toxic effects in liver. Environmental Science & Technology 50, 4054-4060.

Martin, K.L.M., Pierce, E.A., Quach, V.V., Studer, M., Browman, H., 2019. Population trends of beach-spawning California grunion Leuresthes tenuis monitored by citizen scientists. ICES Journal of Marine Science.

Mazurais, D., Ernande, B., Quazuguel, P., Severe, A., Huelvan, C., Madec, L., Mouchel, O., Soudant, P., Robbens, J., Huvet, A., Zambonino-Infante, J., 2015. Evaluation of the impact of polyethylene microbeads ingestion in European sea bass (Dicentrarchus labrax) larvae. Marine Environmental Research 112, 78-85.

Rochman, C.M., Kurobe, T., Flores, I., Teh, S.J., 2014. Early warning signs of endocrine disruption in adult fish from the ingestion of polyethylene with and without sorbed chemical pollutants from the marine environment. Sci. Total Environ. 493, 656-661.

Connectivity of Salt Marsh Physical Characteristics and Small Mammal Ecology in a Southern California Tidal Marsh - Kyra MacFarlane (CSULB; advisor Dr. Christine Whitcraft)

A brown lizard on a white surfaceDescription automatically generated with medium confidence

While many aspects of marsh ecology have been extensively studied in recent decades, little is known about the rodents within southern California’s tidal salt marshes. Like wetlands connecting terrestrial, marine, and freshwater systems, rodents connect terrestrial and aquatic ecosystems as both foragers in the marsh and as an important food source for higher trophic carnivores. Little is known, however, about their species composition, distribution, or diets. To address these knowledge gaps, I (1) trapped rodents at Seal Beach National Wildlife Refuge (SBNWR) along an elevation gradient to assess distribution regarding tidal flux and (2) assessed community composition at two sites with differing elevation profiles and upland habitat connectivity.

Rodent trapping as well as fur, fecal, and vegetation collection occurred from June-December in 2019 and June-November in 2020 with a total of 3888 trap nights per year. Both sites are roughly 210m x 90m in area, with 54 large Sherman traps deployed. Site 1 sits at a higher elevation than site 2 and consists of more mid-marsh to upland habitat while site 2 is characterized by lower elevation and low-marsh vegetation. In 2019, three species were caught, including Mus musculus (house mouse), Reithrodontomys megalotis limicola (southern marsh harvest mouse), and Peromyscus maniculatus (deer mouse), however Peromyscus accounted for only 0.026% of total captures. In 2020, Rattus rattus (black rat) were also captured, but released without tagging, accounting for only 0.009% of captures. As such, analyses are focused only on house mice and the southern marsh harvest mouse (SoMHM).

Between 2019 and 2020, population increases occurred for both house mice and SoMHM, with house mice captures increasing from 141 to 571 and SoMHM captures increasing from 81 to 744. Patterns in capture frequency also varied between the two years. In 2019, captures increased from summer to fall for both species. Captures, regardless of species, were also more frequent during low tide when marsh habitat was exposed. This trend in tide differentiation was not seen in 2020. During 2020, more SoMHM were captured compared to house mice. Trends in captures across seasons also differed between the two species with the majority of SoMHM being caught in the fall and most house mice being caught in the summer. There were also differences by site with more SoMHM caught in site 1 compared to site 2, while house mice were caught in roughly equal numbers at both locations.

These data seem to suggest environmental factors affect mouse abundance and distributions in non-linear ways. Higher abundances in site 1 compared to site 2 for SoMHM across years suggests that mid-marsh to high-marsh habitat may be more suitable. While house mice were more abundant in site 1 in 2019, the nearly equal distribution of mice in 2020 suggests they may be less restricted in habitat preferences.

Samples of rodent fur, feces, and muscle tissue, as well as insects and vegetation from SBNWR have been sent to the UC Davis Stable Isotope Facility and will be analyzed as soon as possible. The results should elucidate the diets of house mice and the southern marsh harvest mouse, to better establish the trophic niche space of these rodents within southern California tidal marshes.

James Chhor picture

Figure 1. Elevation heatmap of sites located at Seal Beach National Wildlife Refuge.

James Chhor picture

Figure 2. Mus musculus (left) and Reithrodontomys megalotis limicola (right) caught and tagged at Seal Beach National Wildlife Refuge.