Effects of Nile perch, Lates niloticus, on functional and specific fish diversity in Uganda's Lake Kyoga system

The introduction of Nile perch, Lates niloticus, to Lake Victoria, East Africa, interacted with eutrophication to cause a reorganization of the lake's food web and the extirpation of many endemic fishes. The Lake Kyoga satellite system lies downstream from Lake Victoria. It encompasses species‐rich lakes where Nile perch are absent or very rare, and low diversity lakes where L. niloticus is abundant. In 1999 we surveyed seven lakes in the Kyoga system using experimental monofilament gill nets (1/4–1 inches variable mesh). At Boston University we assessed δ¹⁵N signatures of epaxial muscle from subsamples of the catch (n = 361). These signatures are often highly correlated with the near‐term mean realized trophic position of an individual organism. A neural network analysis of fish length, species name, trophic level, and lake of origin fish explained 94% of the sample variance in δ¹⁵N. We analysed statistical patterns in these signatures at a number of spatial scales. The relationship between trophic level and δ¹⁵N varied greatly among lakes. Higher diversity perch‐free lakes had greater variance in δ¹⁵N values and fish lengths than lower diversity Nile perch lakes, suggesting an important relationship between species diversity and functional diversity. Against expectations, lake size was negatively correlated with δ¹⁵N. Patterns in stable isotope signatures indicated that Nile perch lakes have shorter food chains than perch‐free lakes. The results throw up two management problems for the Kyoga system. Impacted lakes need to be studied to understand and ameliorate the community‐level effects of Nile perch introduction, whereas the species‐rich nonperch lakes, which harbour a large proportion of the remaining diversity of regionally endemic taxa, are in need of conservation planning.     

The impact of the introduction of Nile perch, Lates niloticus (L.) on the fisheries of Lake Victoria

The piscivorous Nile perch was introduced into Lake Victoria some 30 years ago, since when it has completely transformed the fishing industry and the species composition of the fish fauna of the lake. The original multispecies fishery, based mostly on cichlids (haplochromines, tilapias), cyprinids ( Barbus, Labeo, Rastrineobola ) and siluroids ( Bagrus, Clarias, Synodontis, Schilbe ), has changed dramatically to one based on three species: the introduced Nile perch, the cyprinids, Rastrineobola argenrea (Pellegrin), and the introduced Nile tilapia, Oreochromis niloticus (Linnaeus).
Within 25 years of its introduction the Nile perch became ubiquitous and now occurs in virtually every habitat with the exception of swamps and affluent rivers. It has preyed on all other species with profound effects, especially on the stocks of haplochromines. These originally comprised 80% of the total fish biomass in Lake Victoria, but have now decreased to less than 1% offish catches from the Kenyan waters of the lake. The fishermen of Lake Victoria have adjusted to this ecological crisis by using large-meshed nets to catch Nile perch, which has become the most important commercial species. For the first time in the history of Lake Victoria, fish fillets are now being exported to several overseas countries: the fillets are all from Nile perch.     

Ontogenetic shifts in phenotype–environment associations in Nile perch,Lates niloticus (Perciformes: Latidae) from Lake Nabugabo,Uganda

Habitat‐associated trait divergence may vary across ontogeny if there are strong size‐related shifts in selection pressures. We quantified patterns of phenotypic divergence in Nile perch (Lates niloticus) from ecologically distinct wetland edge and forest edge habitats in Lake Nabugabo, Uganda, and we compared patterns of divergence across three size classes to determine whether trends are consistent through Nile perch ontogeny. We predicted that inter‐habitat variation in biotic (e.g. vegetation structure) and abiotic (e.g. dissolved oxygen concentration) variables may create divergent selective regimes. We compared body morphology using geometric morphometrics and found substantial differences between habitats, although not all trends were consistent across size classes. The most striking aspects of divergence in small Nile perch were in mouth orientation, head size, and development of the caudal region. Medium‐sized Nile perch also showed differences in mouth orientation. Differences in large individuals were related to eye size and orientation, as well as caudal length. The observed patterns of divergence are consistent with functional morphological predictions for fish across divergent trophic regimes, high and low predation environments, and complex and simple habitats. Although this suggests adaptive divergence, the source of phenotypic variation is unknown and may reflect phenotypic plasticity and/or genetic differences. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 449–465.     

Genetic affinities of an introduced predator: Nile perch in Lake Victoria, East Africa

Although the introduction of Nile perch, Lates niloticus , to Lake Victoria has received intense global attention, especially in relation to its impact on endemic cichlid species and on fishery yields, fundamental information on its taxonomy and population genetics is lacking. Most importantly, the introduced fish originated from two lakes (Lakes Albert and Turkana) containing three Lates species, and it has never been entirely clear which of these became established in Lake Victoria, or indeed whether the Lake Victoria population is derived from hybridization between Lates species. In addition, genetic drift caused by the relatively small founder population (≈ 400), the initially slow population increase followed by a period of explosive population growth, and selection pressures in the new environment may have resulted in substantial genetic changes. Allozyme data indicated that the introduced Nile perch of Lake Victoria were mainly L. niloticus from Lake Albert, although maximum likelihood estimates of stock contributions (GSI) suggested the presence of L. macrophthalmus. In contrast, introduced Nile perch in adjacent smaller lakes (Lakes Kyoga and Nabugabo) appeared to be entirely L. niloticus . The effect of the introductions on allozyme diversity varied among lakes and appeared to be uncorrelated to the number of fish introduced.     

The decline of the native fishes of lakes Victoria and Kyoga (East Africa) and the impact of introduced species,especially the Nile perch,Lates niloticus,and the Nile tilapia,Oreochromis niloticus

Synopsis There has been a decline, and in some cases an almost total disappearance, of many of the native fish species of lakes Victoria and Kyoga in East Africa since the development of the fisheries of these lakes was initiated at the beginning of this century. The Nile perch, Lates niloticus, a large, voracious predator which was introduced into these lakes about the middle of the century along with several tilapiine species, is thought to have caused the reduction in the stocks of several species. But overfishing and competition between different species also appear to have contributed to this decline. By the time the Nile perch had become well established, stocks of the native tilapiine species had already been reduced by overfishing. The Labeo victorianus fishery had also deteriorated following intensive gillnetting of gravid individuals on breeding migrations. L. niloticus is, however, capable of preying on the species which haven been overfished and could have prevented their stocks from recovering from overfishing. L. niloticus is also directly responsible for the decline in populations of haplochromine cichlids which were abundant in these lakes before the Nile perch became established. Even without predation by Nile perch, it has been shown that the haplochromine cichlids could not have withstood heavy commercial exploitation if a trawl fishery had been established throughout Lake Victoria. Their utilisation for human food has also posed some problems. The abundance of the native tilapiine species may also have been reduced through competition with introduced species which have similar ecological requirements. At present, the Nile perch and one of the introduced tilapiine species, Oreochromis niloticus, form the basis of the fisheries of lakes Victoria and Kyoga.Invited editorial     

Ecological, environmental and socioeconomic aspects of the Lake Victoria's introduced Nile perch fishery in relation to the native fisheries and the species culture potential: lessons to learn

Inland fishery ecosystems in Africa are characterized by patterns of overexploitation, environmental degradation and exotic species introductions. Ecological complexity and diversity of aquatic habitats dictate that fishes in general are not evenly distributed in a water body. However, fisheries management regimes tend to ignore this basic principle, assume generalized conditions in a water body, and focus more on ‘desired’ objectives such as maximizing catch. The result is to disregard fish habitat boundaries and anthropogenic influences from the catchment that influence fish production. Overexploitation and environmental degradation disrupt sustainable socioeconomic benefits from the fisheries, create uncertainty among investors, but leave some managers calling for more information with the expectation that the fisheries will recover with time. Open access to the fisheries and full control of fishing effort remain challenges for managers. Exotic species introductions and fish farming can increase production, but such interventions require firm commitment to sound ecological principles and strict enforcement of recommended conservation and co‐management measures in capture fisheries. The general tendency to downplay fishing effort issues, other ecosystem values and functions or rely on temperate fisheries models until a new cycle of overexploitation emerges, characterizes many management patterns in inland fisheries. Aquaculture is not an option to challenges in capture fisheries management. Aquaculture should be developed to increase fish production but even this practice may have negative environmental impacts depending on practice and scale. Decades of information on Lake Victoria fisheries trends and aquaculture development did not stop the collapse of native fisheries. The successfully introduced Nile perch (Lates niloticus) has shown signs of overexploitation and aquaculture has again been considered as the option. By reviewing significant trends associated with Nile perch and its feasibility in aquaculture this paper uses Lake Victoria to illustrate ‘special interest management’ targeting selected species of fish rather than the fisheries.     

Growth and reproduction of the Nile perch,Lates niloticus,an introduced predator,in the Nyanza Gulf,Lake Victoria,East Africa

Synopsis Length-frequency data suggest Nile perch, Lates niloticus, from the Nyanza Gulf grew to a total length of 9 cm by age 118 days and 23 cm by age 287 days. A modified von Bertalanffy growth curve _t = 1.35·L(1-e^–K(t-t _o)) with the parameters L = 93.1, K = 0.272 and t_o = 0.046, is suggested to describe growth up to 5 years of age and the relationship _t = 1.35·(31.96 + 7.681t) for fish aged 6 years and above. Length-weight relationships were = 0.0234·-gt^2.74 for fish between 7 and 15.9 cm total length, = 0.0151·^2.94 for fish between 16 and 45.9 cm total length, and = 0.0023·^3.44 for fish between 46 and 120 cm total length. Male Nile perch first matured between 50 and 55 cm total length when they were probably 2 years old; female Nile perch first matured between 80 and 85 cm total length when they were probably 4 years old. Small males were common, large males were rare, with the reverse holding for females. Sex change, from male to female, is a possible explanation for this size dimorphism.     

Divergence in aerobic scope and thermal tolerance is related to local thermal regime in two populations of introduced Nile perch (Lates niloticus)

We tested whether thermal tolerance and aerobic performance differed between two populations of Nile perch (Lates niloticus) originating from the same source population six decades after their introduction into two lakes in the Lake Victoria basin in East Africa. We used short-term acclimation of juvenile fish to a range of temperatures from ambient to +6°C, and performed critical thermal maximum (CT_max) and respirometry tests to measure upper thermal tolerance, resting and maximum metabolic rates, and aerobic scope (AS). Across acclimation temperatures, Nile perch from the cooler lake (Lake Nabugabo, Uganda) tended to have lower thermal tolerance (i.e., CT_max) and lower aerobic performance (i.e., AS) than Nile perch from the warmer waters of Lake Victoria (Bugonga region, Uganda). Effects of temperature acclimation were more pronounced in the Lake Victoria population, with the Lake Nabugabo fish showing less thermal plasticity in most metabolic traits. Our results suggest phenotypic divergence in thermal tolerance between these two introduced populations in a direction consistent with an adaptive response to local thermal regimes.     

Finding complexity in complexes: Assessing the causes of mitonuclear discordance in a problematic species complex of Mesoamerican toads

Mitonuclear discordance is a frequently encountered pattern in phylogeographic studies and occurs when mitochondrial and nuclear DNA display conflicting signals. Discordance among these genetic markers can be caused by several factors including confounded taxonomies, gene flow, and incomplete lineage sorting. In this study, we present a strong case of mitonuclear discordance in a species complex of toads (Bufonidae: Incilius coccifer complex) found in the Chortís Block of Central America. To determine the cause of mitonuclear discordance in this complex, we used spatially explicit genetic data to test species limits and relationships, characterize demographic history, and quantify gene flow. We found extensive mitonuclear discordance among the three recognized species within this group, especially in populations within the Chortís Highlands of Honduras. Our data reveal nuclear introgression within the Chortís Highlands populations that was most probably driven by cyclical range expansions due to climatic fluctuations. Though we determined introgression occurred within the nuclear genome, our data suggest that it is not the key factor in driving mitonuclear discordance in the entire species complex. Rather, due to a lack of discernible geographic pattern between mitochondrial and nuclear DNA, as well as a relatively recent divergence time of this complex, we concluded that mitonuclear discordance has been caused by incomplete lineage sorting. Our study provides a framework to test sources of mitonuclear discordance and highlights the importance of using multiple marker types to test species boundaries in cryptic species.     

Potential fishery of Nile perch Lates niloticus Linne (Pisces: Centropomidae) in Nyanza Gulf of Lake Victoria,East Africa

From bottom trawls, Lates niloticus (Lin.) in Nyanza Gulf was observed to have a gulf-wide distribution. Lates dominated the catch at Homa point. Catch rates in kg h^-1 varied from one location to another and from month to month.Its estimated production is 11 000 metric tons, netting about 22 000 000 Kenya shillings (US $2 000 000).Abundance of food items such as freshwater shrimps of the genus Caridina, and Engraulicypris argenteus, have been used as basis for estimating the growth and production of Lates.     

Neuromusculature of Gyrodactylus rysavyi, a monogenean gill and skin parasite of the catfish Clarias gariepinus

Phalloidin fluorescence technique, enzyme cytochemistry and immunocytochemistry in conjunction with confocal scanning laser microscopy were used for the first time to describe the nervous and muscle systems of the viviparous monogenean parasite, Gyrodactylus rysavyi inhabiting the gills and skin of the Nile catfish Clarias gariepinus. The body wall muscles are composed of an outer layer of circular fibres, an intermediate layer of paired longitudinal fibres and an inner layer of well-spaced bands of diagonal fibres arranged in two crossed directions. The musculature of the pharynx, intestine, reproductive tract and the most prominent muscles of the haptor were also described. Two characteristic muscular pads were found lying in the anterior region of the haptor in close contact with the hamuli. To each one of these pads, a group of ventral extrinsic muscles was connected. The role of this ventral extrinsic muscle in the body movement was discussed. The mechanism operating the marginal hooklets was also discussed. The central nervous system (CNS) consists of paired cerebral ganglia from which three pairs of longitudinal ventral, lateral and dorsal nerve cords arise. The nerve cords are connected at intervals by many transverse connectives. The CNS is better developed ventrally than dorsally or laterally and it has the highest reactivity for all neuroactive substances examined. Both the central and the peripheral nervous system (PNS) are bilaterally symmetrical. Structural and functional correlates of the neuromusculature of the pharynx, haptor and reproductive tracts were explained. The results implicated acetylcholine, FMRFamide-related peptides (FaRPs) and serotonin in sensory and motor function. The results were compared with those of the monogeneans Macrogyrodactylus clarii and M. congolensis inhabiting the gills and skin respectively of the same host fish C. gariepinus.     

Reproductive potential of the Nile perch,Lates niloticus L. and the establishment of the species in Lakes Kyoga and Victoria (East Africa)

The size at first maturity, sex ratio and fecundity of L. niloticus in Lake Kyoga have been examined, and compared with the situation in other aquatic systems. The species has the ability to reproduce enormously. It produces up to 16 million eggs. In Lake Kyoga, fecundity (F) increases with length (L) in cm according to the equation: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaciOraiaac2% dacaGGGaGaaiinaiaac6cacaGG0aGaai4maiaacAdacaGGGaGaaiiE% aiaacccacaGGXaGaaiimamaaCaaaleqabaGaaiylaiaacAdaaaGcca% GGmbWaaWbaaSqabeaacaGGYaGaaiOlaiaacMdacaGGYaaaaaaa!44D8!\[\operatorname{F} = 4.436 x 10^{ - 6} L^{2.92} \]Information from different habitats shows that females grow to a larger size than males but the growth rate is the same in both sexes. Males mature earlier than females at 50–65 cm total length with females maturing between 60–95 cm. There are about twice as many males as females. The rapid establishment of L. niloticus in Lake Kyoga and the Nyanza Gulf of Lake Victoria following its introduction is attributed to the high reproductive potential of the species under favourable environmental conditions.     

Changes in the prey ingested and the variations in the Nile perch and other fish stocks of Lake Kyoga and the northern waters of Lake Victoria (Uganda)

The fish stocks of Lakes Kyoga and Victoria have changed since Nile perch, Lates niloticus (L.), was introduced, and this is reflected in the prey ingested by the predator. Initially, haplochromine cichlids constituted the main prey of most sizes of Nile perch. As the stocks of these have declined, Caridina nilotica (Roux) and Anisopteran nymphs have become the dominant food of the juveniles, while Rastrineobola argentea (Pellegrin), juvenile Nile perch and Oreochromis niloticus (L.) have become the main food of larger Nile perch. Apart from R. argentea , most of the native fish species of these lakes have disappeared. The stocks of Nile perch in Lake Kyoga, to which it was introduced earlier than to Lake Victoria, have declined after dominating the fishery since 1965. and have been superseded by O. niloricus . an introduced herbivore. Similar changes are now occurring in Lake Victoria. The Nile perch might not maintain the high yield realized in the two lakes when haplochromines were abundant. It is therefore necessary to exercise caution with high and long-term investments aimed specifically at developing the Nile perch fishery.     

Changes in the feeding biology of the Nile perch, Lates niloticus (L.) (Pisces: Centropomidae), in Lake Victoria, East Africa since its introduction in 1960, and its impact on the native fish community of the Nyanza Gulf

Lates niloticus is not native to Lake Victoria but was introduced during or shortly before 1960. It remained relatively uncommon until 1975, when the number in the Nyanza Gulf began to increase impressively, the estimated catch rising over 100-fold between 1978 and 1982. Originally Lates was piscivorous, its diet reflecting the composition of the native fish community. The present investigation has revealed that its diet is now almost entirely comprised of Caridina nilotica , a small microphagous prawn, and juvenile Lates. Native fish species, except for the small pelagic Rastrineobola argenteus , are very rarely consumed. This change in diet is a result of the shattering impact Lates predation has had on the native fishes, which have been virtually wiped out. The original community, which was dominated by several hundred haplochromine species and the catfishes Clarias mossambicus and Bagrus docmac which preyed upon them, and included two endemic tilapiine cichlids and 38 species of non-cichlids, no longer exists. It has been replaced by a community dominated by Lates which now accounts for well over 80% of the fish biomass in the Nyanza Gulf and very nearly 100% in the study area. The only other species regularly encountered were Oreochromis niloticus , an introduced tilapiine, and Rastrineobola argenteus , a native zooplanktivore.     

Phylogeography of a Holarctic nematode, Soboliphyme baturini, among mustelids: climate change, episodic colonization, and diversification in a complex host–parasite system

Phylogeography of Soboliphyme baturini , a nematode parasite in mustelids, is explored across Beringia. Sequences of the mitochondrial cytochrome c oxidase subunit I and nicotinamide adenine dinucleotide dehydrogenase subunit 4 genes were evaluated from 37 S. baturini , representing 19 localities throughout Alaska, Canada, and Siberia. A total of 30 haplotypes was recovered and maximum parsimony and Bayesian phylogenetic analyses support the recognition of a single species with a distribution extending from the Palearctic to the Nearctic. Within S. baturini , a host-specific partition in North America between Martes caurina and Martes americana was not identified. Instead, substantial geographic structure within S. baturini relates to the dynamic geological history of this northern region and especially the North Pacific Coast. Beringia and other coastal refugia along the western margin of North America played a large role during stadial maxima in the persistence and divergence of the parasite. Repeated events for biotic expansion and geographic colonization across the Bering Land Bridge and the Holarctic during glacial maxima in the Pleistocene appear to have facilitated at least two episodes of host-switching of this nematode among mustelids in populations now distributed in eastern Beringia.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 651–663.     

Light and electronic observations on Henneguya ghaffari (Myxosporea,Bivalvulida) infecting the gills and intestine of Nile perch Lates niloticus (Pisces: Teleostei) from Chad and Senegal

Henneguya ghaffari Ali, 1999, described for the first time in Egypt, has been found on gills and intestine of Nile perch Lates niloticus L. from Chad and Senegal (Africa). It formed plasmodia which induced lesions of infected tissues. In fresh state, the spore body was ovoid and its size was 11.07 +/- 0.7 (range 11 to 13) x 7.7 +/- 0.4 (range 7 to 8) microm. The length of the caudal appendages was 44.2 +/- 1.7 (42 to 48) microm. The polar capsules were pyriform, of equal size, with the polar filament showing 4 coils, and measuring 3.17 +/- 0.1 (range 3 to 4) x 2.2 +/- 0.1 (range 1 to 2) microm. The total length of the spore was 55.73 +/- 1.7 (range 53 to 61) microm. At ultrastructural level, our results confirm that in Henneguya species, the sporoplasm is binucleate and the pansporaoblast is disporous.     

Parasite loss and introduced species: a comparison of the parasites of the Puerto Rican tree frog, (<Emphasis Type="Italic">Eleutherodactylus coqui</Emphasis>), in its native and introduced ranges

The Puerto Rican frog, Eleutherodactylus coqui has invaded Hawaii and reached densities far exceeding those in their native range. One possible explanation for the success of E. coqui in its introduced range is that it lost its co-evolved parasites in the process of the invasion. We compared the parasites of E. coqui in its native versus introduced range. We collected parasite data on 160 individual coqui frogs collected during January-April 2006 from eight populations in Puerto Rico and Hawaii. Puerto Rican coqui frogs had higher species richness of parasites than Hawaiian coqui frogs. Parasite prevalence and intensity were significantly higher in Hawaii, however this was likely a product of the life history of the dominant parasite and its minimal harm to the host. This suggests that the scarcity of parasites may be a factor contributing to the success of Eleutherodactylus coqui in Hawaii.     

PERMANENT GENETIC RESOURCES: Isolation and characterization of microsatellite loci in the cichlid fish in Lake Victoria, Haplochromis chilotes

Twelve short tandem repeat markers were successfully isolated from a cichlid, Haplochromis chilotes, in Lake Victoria, and characterized in Haplochromis pyrrhocephalus. The microsatellite regions of these markers were found to have between two and 48 alleles with heterozygosity ranging from 0.07 to 0.97. No loci showed significant departures from the Hardy–Weinberg or linkage equilibrium after the Bonferroni correction (P > 0.05). Cross‐species amplification in other cichlids of Lake Victoria, Haplochromis laparogramma, Lithochromis rubripinnis, L. rufus and Haplochromis sp. ‘rockkribensis’, was successful.     

“灭非灵”对尼罗罗非鱼鳃、肝和肾组织结构的影响

通过"灭非灵"对尼罗罗非鱼(Oreochromis niloticus)(体重为34.65±5.69 g)的急性毒性试验及对鳃、肝、肾的组织学研究,从组织学角度探讨了"灭非灵"对尼罗罗非鱼的致死机理。结果表明:"灭非灵"对尼罗罗非鱼的24、48、72和96 h-LC50分别为0.148、0.103、0.048和0.032 mg·L-1;其组织病理学损伤表现为鳃小片萎缩、卷曲、坏死、脱落和融合,鳃间隙分泌大量的粘液细胞;肝细胞肿大,空泡化,细胞界限模糊,细胞核固缩;肾细胞肿大,充血;"灭非灵"对3种组织的损伤程度为鳃肝脏肾脏,3种组织的损伤很有可能是造成尼罗罗非鱼死亡的主要原因。     

Multispecies interactions among a plant parasite,a pollinator and a seed predator affect the reproductive output of an invasive plant,Cytisus scoparius

Interactions between species pairs are almost always mediated by interactions with other species. The outcomes of these multispecies interactions are often difficult to predict and are rarely studied. In addition to their theoretical importance, multispecies interactions are also important for management situations. Where multiple agents are used to control invasive species, interactions between agents may either enhance or reduce the impacts on the target species, or may simply have additive effects. In this study, conducted in a Mediterranean‐type woodland in Australia, we examined how the interaction between an invasive legume, Cytisus scoparius (Leguminosae), its pollinator, Apis mellifera and a seed predator, Bruchidius villosus (Bruchidae), are modified by a native hemiparasitic vine, Cassytha pubescens (Loranthaceae). The parasite had a direct negative effect on C. scoparius, reducing flowering by 50% and consequently fruit and seed production. Despite having fewer flowers, infected plants had the same proportion of ‘tripped’ flowers, an indirect measure of pollinator visitation, as uninfected plants; although fruit formed on infected plants it was more likely to abort prematurely. Seed predation by B. villosus was lower on parasite‐infected C. scoparius plants than in uninfected plants. Although Ca. pubescens had an antagonistic effect on B. villosus, in consort, the two agents reduced overall seed production by an average of 62%. The acquired parasite Ca. pubescens was more effective in reducing reproductive output than the introduced seed predator, B. villosus, and shows potential as a biocontrol agent for C. scoparius. We documented a subadditive effect of two biological enemies on the invasive species, where the acquired parasite had a stronger effect than the introduced seed predator.