Tommy L. F. Leung

University of New England

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Fossils of parasites: what can the fossil record tell us about the evolution of parasitism?

Biological reviews/Biological reviews of the Cambridge Philosophical Society (2015)

Tommy L. F. Leung

Parasites are common in many ecosystems, yet because of their nature, they do not fossilise readily and are very rare in the geological record. This makes it challenging to study the evolutionary transition that led to the evolution of parasitism in different taxa. Most studies on the evolution of parasites are based on phylogenies of extant species that were constructed based on morphological and molecular data, but they give us an incomplete picture and offer little information on many important details of parasite-host interactions. The lack of fossil parasites also means we know very little about the roles that parasites played in ecosystems of the past even though it is known that parasites have significant influences on many ecosystems. The goal of this review is to bring attention to known fossils of parasites and parasitism, and provide a conceptual framework for how research on fossil parasites can develop in the future. Despite their rarity, there are some fossil parasites which have been described from different geological eras. These fossils include the free-living stage of parasites, parasites which became fossilised with their hosts, parasite eggs and propagules in coprolites, and traces of pathology inflicted by parasites on the host's body. Judging from the fossil record, while there were some parasite-host relationships which no longer exist in the present day, many parasite taxa which are known from the fossil record seem to have remained relatively unchanged in their general morphology and their patterns of host association over tens or even hundreds of millions of years. It also appears that major evolutionary and ecological transitions throughout the history of life on Earth coincided with the appearance of certain parasite taxa, as the appearance of new host groups also provided new niches for potential parasites. As such, fossil parasites can provide additional data regarding the ecology of their extinct hosts, since many parasites have specific life cycles and transmission modes which reflect certain aspects of the host's ecology. The study of fossil parasites can be conducted using existing techniques in palaeontology and palaeoecology, and microscopic examination of potential material such as coprolites may uncover more fossil evidence of parasitism. However, I also urge caution when interpreting fossils as examples of parasites or parasitism-induced traces. I point out a number of cases where parasitism has been spuriously attributed to some fossil specimens which, upon re-examination, display traits which are just as (if not more) likely to be found in free-living taxa. The study of parasite fossils can provide a more complete picture of the ecosystems and evolution of life throughout Earth's history.

Fossil Record

10.1111/brv.12238

Cite

Citations (65)

Evolution: How a Barnacle Came to Parasitise a Shark

Current Biology (2014)

Tommy L. F. Leung

Thoracica

10.1016/j.cub.2014.05.008

Cite

Citations (5)

Effects of interspecific competition on asexual proliferation and clonal genetic diversity in larval trematode infections of snails

Parasitology (2008)

Devon B. Keeney Sanne Boessenkool Tania M. King Tommy L. F. Leung Robert Poulin

SUMMARY Interactions among different parasite species within hosts can be important factors shaping the evolution of parasite and host populations. Within snail hosts, antagonistic interactions among trematode species, such as competition and predation, can influence parasite abundance and diversity. In the present study we examined the strength of antagonistic interactions between 2 marine trematodes ( Maritrema novaezealandensis and Philophthalmus sp.) in naturally infected Zeacumantus subcarinatus snails. We found approximately the same number of snails harbouring both species as would be expected by chance given the prevalence of each. However, snails infected with only M. novaezealandensis and snails with M. novaezealandensis and Philophthalmus sp. co-occurring were smaller than snails harbouring only Philophthalmus sp. In addition, the number of Philophthalmus sp. rediae was not affected by the presence of M. novaezealandensis sporocysts and the within-host clonal diversity of M. novaezealandensis was not influenced by the presence of Philophthalmus sp. Our results suggest that antagonistic interactions may not be a major force influencing the evolution of these trematodes and that characteristics such as host size and parasite infection longevity are shaping their abundance and population dynamics.

Asexual reproduction

10.1017/s0031182008004435

Cite

Citations (24)

Size-dependent pattern of metacercariae accumulation in Macomona liliana: the threshold for infection in a dead-end host

Parasitology Research (2008)

Tommy L. F. Leung Robert Poulin

10.1007/s00436-008-1166-2

Cite

Citations (19)

Body size, trophic level, and the use of fish as transmission routes by parasites

Oecologia (2011)

Robert Poulin Tommy L. F. Leung

10.1007/s00442-011-1906-3

Cite

Citations (75)

Contribution of parasites to intra- and inter-site variation in shell morphology of a marine gastropod

Journal of the Marine Biological Association of the United Kingdom (2008)

David W. Thieltges Ian Saldanha Tommy L. F. Leung Robert Poulin

In gastropods, variation in shell morphology can be caused by the action of several biotic and abiotic factors. While much of this variation is seen in comparisons between different sites or populations, there is also substantial variation in shell morphology among individuals living side by side. We investigate the effect of trematode parasitism on both intra- as well as inter-site variation in the morphology of the New Zealand whelk Cominella glandiformis . We found that both infection by the trematode Curtuteria australis and site of origin had significant effects on several morphometric dimensions of the snail shell, with some interactions between the two factors. On its own, infection by C. australis accounted for 20 to 60% of the variance in shell morphology, depending on the dimension measured. Infected snails also had smoother shells, with less prominent ridges, than their uninfected conspecifics. Other trematode species, infecting whelks at much lower prevalence, also had impacts on shell morphology, but not necessarily in the same direction as C. australis . Overall, parasitism may be an important factor in explaining intra- and inter-site variation in snail phenotype, with potential repercussions for snail populations and their interactions with other community members.

Whelk

Morphology

Morphometrics

10.1017/s0025315408002294

Cite

Citations (13)

Recruitment rate of gymnophallid metacercariae in the New Zealand cockle Austrovenus stutchburyi: an experimental test of the hitch-hiking hypothesis

Parasitology Research (2007)

Tommy L. F. Leung Robert Poulin

Cockle

10.1007/s00436-007-0479-x

Cite

Citations (12)

Parasite Diversity and Diversification: Patterns of diversity and distribution of aquatic invertebrates and their parasites

Tommy L. F. Leung Camilo Mora Klaus Rohde

Source

Cite

Citations (0)

Counting Protests in News Articles: A Dataset and Semi-Automated Data Collection Pipeline

arXiv (Cornell University) (2021)

Tommy L. F. Leung L. Nathan Perkins

Between January 2017 and January 2021, thousands of local news sources in the United States reported on over 42,000 protests about topics such as civil rights, immigration, guns, and the environment. Given the vast number of local journalists that report on protests daily, extracting these events as structured data to understand temporal and geographic trends can empower civic decision-making. However, the task of extracting events from news articles presents well known challenges to the NLP community in the fields of domain detection, slot filling, and coreference resolution. To help improve the resources available for extracting structured data from news stories, our contribution is three-fold. We 1) release a manually labeled dataset of news article URLs, dates, locations, crowd size estimates, and 494 discrete descriptive tags corresponding to 42,347 reported protest events in the United States between January 2017 and January 2021; 2) describe the semi-automated data collection pipeline used to discover, sort, and review the 144,568 English articles that comprise the dataset; and 3) benchmark a long-short term memory (LSTM) low dimensional classifier that demonstrates the utility of processing news articles based on syntactic structures, such as paragraphs and sentences, to count the number of reported protest events.

Benchmark (surveying)

Sentiment Analysis

Coreference

10.48550/arxiv.2102.00917

Cite

Citations (6)

Interactions between parasites of the cockleAustrovenus stutchburyi: hitch-hikers, resident-cleaners, and habitat-facilitators

Parasitology (2006)

Tommy L. F. Leung Robert Poulin

The patterns of association between parasites within a particular host are determined by a number of factors. One of these factors is whether or not infection by one parasite influences the probability of acquiring other parasite species. This study investigates the pattern of association between various parasites of the New Zealand cockle Austrovenus stutchburyi. Hundreds of cockles were collected from one locality within Otago Harbour, New Zealand and examined for trematode metacercariae and other symbionts. Two interspecific associations emerged from the study. First, the presence of the myicolid copepod Pseudomyicola spinosus was positively associated with higher infection intensity by echinostomes. The side-effect of the copepod's activities within the cockle is suggested as the proximate mechanism that facilitates infection by echinostome cercariae, leading to a greater rate of accumulation of metacercariae in cockles harbouring the copepod. Second, a positive association was also found between infection intensity of the metacercariae of foot-encysting echinostomes and that of gymnophallid metacercariae. This supports earlier findings and suggests that the gymnophallid is a hitch-hiker parasite because, in addition to the pattern of positive association, it (a) shares the same transmission route as the echinostomes, and (b) unlike the echinostomes, it is not capable of increasing the host's susceptibility to avian predation. Thus, both active hitch-hiking and incidental facilitation lead to non-random infection patterns in this parasite community.

Cockle

10.1017/s0031182006001478

Cite

Citations (28)