Papers by María Ocasio Torres
Predators can induce a suit of evolutionary responses, such as changes in behavior, life-history ... more Predators can induce a suit of evolutionary responses, such as changes in behavior, life-history traits or morphology, from their prey. Our work adds to the growing number of studies of kairomone-mediated aquatic predator–prey interactions that significantly affect prey morphology. Individuals of the amphidromous shrimp Xiphocaris elongata have elongated rostrums below geomorphic barriers where predatory fishes are present and short rostrums in stream reaches above geomorphic barriers where predatory fishes are absent. Our objective was to test whether the elongated rostrum in X. elongata is a phenotypic modification induced by kairomones from predatory fish or alarm cues from conspecifics. We cut the rostrums of juvenile, long-rostrum adult, and short-rostrum adult X. elongata and exposed the shrimp to predatory fish fed flakes, predatory fish fed X. elongata, predatory fish fed Atya, the nonpredatory fish S. plumieri, no fish with filtered water, and no fish with stream water. We measured the carapace length and the post-orbital carapace length (to obtain the rostrum length) of every shrimp every 2 wk for a total of 10 times/shrimp. Rostrums of X. elongata exposed to predatory fish fed flakes, predatory fish fed X. elongata, and predatory fish fed Atya shrimp grew longer rostrums than X. elongata exposed to the nonpredatory fish, filtered water, or stream water. Rostrums of juveniles grew faster than those of adults independent of treatment. Rostrum growth was not affected by the treatment × phenotype interaction. These results demonstrate that the elongated rostrum in the amphidromous X. elongata is a phenotypic response induced by kairomones from predatory fish.
The design of transport paths in consuming entities that use routes to access food should be unde... more The design of transport paths in consuming entities that use routes to access food should be under strong selective pressures to reduce costs and increase benefits. We studied the adaptive nature of branching angles in foraging trail networks of the two most abundant tropical leaf-cutting ant species. We mathematically assessed how these angles should reflect the relative weight of the pressure for reducing either trail maintenance effort or traveling distances. Bifurcation angles of ant foraging trails strongly differed depending on the location of the nests. Ant colonies in open areas showed more acute branching angles, which best shorten travel distances but create longer new trail sections to maintain than a perpendicular branch, suggesting that trail maintenance costs are smaller compared to the benefit of reduced traveling distance. Conversely, ant colonies in forest showed less acute branching angles, indicating that maintenance costs are of larger importance relative to the benefits of shortening travel distances. The trail pattern evident in forests may be attributable to huge amounts of litterfall that increase trail maintenance costs, and the abundant canopy cover that reduces traveling costs by mitigating direct sunlight and rain. These results suggest that branching angles represent a trade-off between reducing maintenance work and shortening travel distances, illustrating how animal constructions can adjust to diverse environmental conditions. This idea may help to understand diverse networks systems, including urban travel networks.
Predators may affect prey through inducible defences that can alter prey phenotype. The shrimp Xi... more Predators may affect prey through inducible defences that can alter prey phenotype. The shrimp Xiphocaris elongata exhibits a short rostrum (SR) in the absence of fish predators and a long rostrum (LR) in their presence. The long rostrum in X. elongata is inducible by the predatory fish Agonostomus monticola (mountain mullet). Our objective was to test whether the long rostrum is an effective antipredator defence against A. monticola in different stages of predator–prey interactions (i.e. choice, attacks, bites, rejections, handling time and survival). We conducted behavioural experiments in fish tanks in which we fed A. monticola simultaneously with (1) one LR shrimp and one SR shrimp, or (2) one LR shrimp and one shrimp which originally had a long rostrum but whose rostrum was cut (LR[S]). We scored the fish behaviours in terms of choice, unsuccessful attacks, bites, rejections and handling time. We also conducted mortality experiments in closed artificial pools in which we exposed (1) 10 LR and 10 SR shrimp or (2) 10 LR and 10 LR[S] shrimp to A. monticola, and quantified shrimp survival after 24 h. In the trials with LR and SR shrimp, A. monticola tended to attack SR shrimp first. LR shrimp were unsuccessfully attacked, bitten and rejected more than SR individuals. Handling time was higher for LR shrimp. The mortality experiments show higher survival of LR shrimp. In the trials with LR and LR[S] shrimp, A. monticola tended to attack LR[S] shrimp first. Unsuccessful attacks were similar for LR and LR[S]. There were more bites and rejections and longer handling time for LR shrimp. Survival was similar for LR and LR[S] shrimp in the mortality experiments. This study provides evidence in support of the hypothesis that the long rostrum in X. elongata is an effective antipredator defence against A. monticola by conferring benefits in most stages of the predator–prey interactions.
The role of inducible defences in trophic cascades is poorly understood. The shrimp shredder Xiph... more The role of inducible defences in trophic cascades is poorly understood. The shrimp shredder Xiphocaris elongata has a short rostrum in the absence of predatory fishes and a long rostrum in their presence. The long rostrum in X. elongata is a morphological defence that is inducible by the predatory fish Agonostomus monticola (mountain mullet). Our objective was to measure the effect of fish presence and absence and shrimp phenotype (long rostrum versus short rostrum) on the foraging behaviour of X. elongata and on the decomposition of leaves of the riparian tree Cecropia schreberiana, including their potential for direct or trait-mediated top-down trophic cascades effects. Experiments were carried out in wading pools in which leaf discs of C. schreberiana were exposed for 24 days to processing by either microbes or short-rostrum or long-rostrum X. elongata in either the presence or absence of the predatory fish A. monticola. Shrimp foraging activities, shrimp survival and leaf decomposition were quantified. Shrimp density was not affected by fish presence. However, fish presence decreased foraging activity of long-rostrum X. elongata presumably by increasing their use of refugia throughout the experiments. The foraging of short-rostrum shrimps did not respond to fish presence. The fraction of leaf mass remaining was significantly higher when shrimps were in the presence of fish than when fish were absent, particularly when short-rostrum shrimps were shredding leaves. Shrimps decreased the fraction of mass remaining of C. schreberiana more than the effect of microbial colonisation alone. These results demonstrate that the presence of the predatory fish A. monticola can create trait-mediated top-down trophic cascades in the presence of short-rostrum X. elongata. This study provides evidence that predators have different effects on prey with morphological inducible defences than prey without defences and that these interactions may have critical consequences for other trophic levels.
The amphidromous shrimp Xiphocaris elongata (Guérin-Méneville, 1855) has a long rostrum in the pr... more The amphidromous shrimp Xiphocaris elongata (Guérin-Méneville, 1855) has a long rostrum in the presence of predatory fishes and a short rostrum above steep waterfalls where predatory fishes are absent, i.e., typically above waterfalls. Prior experiments showed that elongated rostrum in X. elongata is induced by chemical signals from the predatory fish Agonostomus monticola. We tested the hypothesis that in addition to rostrum length there are other morphometric differences between long-rostrum (LR) and short-rostrum (SR) X. elongata. We measured the post-orbital carapace length and pleon length of LR and SR shrimp and weighed both shrimp morphs. LR shrimp have significantly longer and heavier pleons than the SR shrimp. These allometric differences may affect the behavior of X. elongata shrimp in ways that, in turn, affect their interactions with predators and the environment. Our study demonstrates the importance of taking pleon measurements when studying crustaceans given that these measurements have been mostly overlooked, and may provide insight of environmental influences on crustacean morphology and behavior. This research provides data of the differences between prey phenotypes, which may alter their life-histories and interactions with the environment.
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Papers by María Ocasio Torres