An overview of vinasse pollution in aquatic ecosystems in Brazil.

We review the negative impacts of vinasse, a byproduct of alcohol distillation, on Brazil's freshwater ecosystems. We found a total of 37 pollution events between the years 1935 and 2023, with this number almost certainly an underestimate due to underreporting and/or unassessed events. Pollution by vinasse occurred both through accidents (e.g., tank failure) and deliberately (i.e., opening of floodgates), although in many cases the causes remain undetermined. All pollution events caused fish kills, with some records reporting negative effects on other organisms as well (i.e., crustaceans and reptiles). Pollution by vinasse, and associated negative effects, was reported for 11 states, with a notable number of cases in São Paulo. Most cases of vinasse pollution and negative impacts on biodiversity were recorded in rivers, followed by streams and reservoirs. Some of the affected river systems harbour threatened freshwater fishes. Hydrological connectivity means that pollution could have propagated along watercourses. Given these consequences of vinasse pollution on biodiversity, ecosystem functioning and services, we recommend a number of remedial actions.

Irrigation dams threaten Brazilian biodiversity.

Brazil is among the main contributors to global biodiversity, which, in turn, provides extensive ecosystem services. Agriculture is an activity that benefits greatly from these ecosystem services, but at the same time is degrading aquatic and terrestrial ecosystems and eroding Brazilian biodiversity. This conflict is growing, as emerging unsustainable legislative proposals that will benefit the agricultural sector are likely to accelerate the decline of biodiversity. One such initiative (Bill 1282/2019) would change Brazil's "Forest Code" (Law 12,651/2012) to facilitate construction of irrigation dams in Permanent Preservation Areas, a category that includes strips (with or without vegetation) along the edges of watercourses. Two other similar bills are advancing through committees in the Chamber of Deputies. Here we provide details of these three bills and discuss their consequences for Brazil's biodiversity if they are approved. Expected negative impacts with changes in the legislation include: increased deforestation; siltation; habitat fragmentation; introduction of non-native species; reduction in the availability of aquatic habitats; and changes in biogeochemical process. These proposals jeopardize biodiversity and may compromise the negotiations for an agreement between Mercosur and the European Union.

Scientists' warning to humanity on the freshwater biodiversity crisis.

Freshwater ecosystems provide irreplaceable services for both nature and society. The quality and quantity of freshwater affect biogeochemical processes and ecological dynamics that determine biodiversity, ecosystem productivity, and human health and welfare at local, regional and global scales. Freshwater ecosystems and their associated riparian habitats are amongst the most biologically diverse on Earth, and have inestimable economic, health, cultural, scientific and educational values. Yet human impacts to lakes, rivers, streams, wetlands and groundwater are dramatically reducing biodiversity and robbing critical natural resources and services from current and future generations. Freshwater biodiversity is declining rapidly on every continent and in every major river basin on Earth, and this degradation is occurring more rapidly than in terrestrial ecosystems. Currently, about one third of all global freshwater discharges pass through human agricultural, industrial or urban infrastructure. About one fifth of the Earth's arable land is now already equipped for irrigation, including all the most productive lands, and this proportion is projected to surpass one third by midcentury to feed the rapidly expanding populations of humans and commensal species, especially poultry and ruminant livestock. Less than one fifth of the world's preindustrial freshwater wetlands remain, and this proportion is projected to decline to under one tenth by midcentury, with imminent threats from water transfer megaprojects in Brazil and India, and coastal wetland drainage megaprojects in China. The Living Planet Index for freshwater vertebrate populations has declined to just one third that of 1970, and is projected to sink below one fifth by midcentury. A linear model of global economic expansion yields the chilling prediction that human utilization of critical freshwater resources will approach one half of the Earth's total capacity by midcentury. Although the magnitude and growth of the human freshwater footprint are greater than is generally understood by policy makers, the news media, or the general public, slowing and reversing dramatic losses of freshwater species and ecosystems is still possible. We recommend a set of urgent policy actions that promote clean water, conserve watershed services, and restore freshwater ecosystems and their vital services. Effective management of freshwater resources and ecosystems must be ranked amongst humanity's highest priorities.

Increases in local richness (α-diversity) following invasion are offset by biotic homogenization in a biodiversity hotspot.

The world's ecosystems are experiencing unparalleled rates of biodiversity change, with invasive species implicated as one of the drivers that restructure local assemblages. Here we focus on the processes leading to biodiversity change in a biodiversity hotspot, the Brazilian Cerrado. The null expectation that invasion leads to increase in local species richness is supported by our investigation of the grass layer in two key habitats (campo sujo and campo úmido). Our analysis uncovered a linear relationship between total richness and invasive richness at the plot level. However, because the invasive species-even though few in number-are widespread, their contribution to local richness (α-diversity) is offset by their homogenizing influence on composition (ß-diversity). We thus identify a mechanism that can help explain the paradox that species richness is not declining in many local assemblages, yet compositional change is exceeding the predictions of ecological theory. As such, our results emphasize the importance of quantifying both α-diversity and ß-diversity in assessments of biodiversity change in the contemporary world.

Gradients in predation risk in a tropical river system.

The importance of predation risk as a key driver of evolutionary change is exemplified by the Northern Range in Trinidad, where research on guppies living in multiple parallel streams has provided invaluable insights into the process of evolution by natural selection. Although Trinidadian guppies are now a textbook example of evolution in action, studies have generally categorized predation as a dichotomous variable, representing high or low risk. Yet, ecologists appreciate that community structure and the attendant predation risk vary substantially over space and time. Here, we use data from a longitudinal study of fish assemblages at 16 different sites in the Northern Range to quantify temporal and spatial variation in predation risk. Specifically we ask: 1) Is there evidence for a gradient in predation risk? 2) Does the ranking of sites (by risk) change with the definition of the predator community (in terms of species composition and abundance currency), and 3) Are site rankings consistent over time? We find compelling evidence that sites lie along a continuum of risk. However, site rankings along this gradient depend on how predation is quantified in terms of the species considered to be predators and the abundance currency is used. Nonetheless, for a given categorization and currency, rankings are relatively consistent over time. Our study suggests that consideration of predation gradients will lead to a more nuanced understanding of the role of predation risk in behavioral and evolutionary ecology. It also emphasizes the need to justify and report the definition of predation risk being used.

Sociability between invasive guppies and native topminnows.

The role of interspecific social interactions during species invasions may be more decisive than previously thought. Research has revealed that invasive fish improve their foraging success by shoaling with native Mexican species, and potentially increase the chances of invasion success. However, do native individuals tend to associate with invaders as well? We tested the hypothesis that the twoline skiffia (Neotoca bilineata) and the Lerma livebearer (Poeciliopsis infans), both native endemic Mexican topminnows, will associate with guppies, a notorious invasive species present in Mexico. Our investigation shows that guppies, twoline skiffias and Lerma livebearers have a mutual tendency to associate with each other. Although there is a marked tendency to shoal with heterospecifics in this system, shoaling partners do not necessarily benefit equally from the association. Further research on invasive-native social interactions is needed to promote our understanding of potential facilitation by natives.

Reasons for the invasive success of a guppy (Poecilia reticulata) population in Trinidad.

The introduction of non-native species into new habitats poses a major threat to native populations. Of particular interest, though often overlooked, are introductions of populations that are not fully reproductively isolated from native individuals and can hybridize with them. To address this important topic we used different approaches in a multi-pronged study, combining the effects of mate choice, shoaling behaviour and genetics. Here we present evidence that behavioural traits such as shoaling and mate choice can promote population mixing if individuals do not distinguish between native and foreign conspecifics. We examined this in the context of two guppy (Poecilia reticulata) populations that have been subject to an introduction and subsequent population mixing event in Trinidad. The introduction of Guanapo River guppies into the Turure River more than 50 years ago led to a marked reduction of the original genotype. In our experiments, female guppies did not distinguish between shoaling partners when given the choice between native and foreign individuals. Introduced fish are therefore likely to benefit from the protection of a shoal and will improve their survival chances as a result. The additional finding that male guppies do not discriminate between females on the basis of origin will further increase the process of population mixing, especially if males encounter mixed shoals. In a mesocosm experiment, in which the native and foreign populations were allowed to mate freely, we found, as expected on the basis of these behavioural interactions, that the distribution of offspring genotypes could be predicted from the proportions of the two types of founding fish. This result suggests that stochastic and environmental processes have reinforced the biological ones to bring about the genetic dominance of the invading population in the Turure River. Re-sampling the Turure for genetic analysis using SNP markers confirmed the population mixing process and showed that it is an on-going process in this river and has led to the nearly complete disappearance of the original genotype.

Heterospecific harassment of native endangered fishes by invasive guppies in Mexico.

Persistent courtship by male Trinidadian guppies (Poecilia reticulata) is costly for conspecific females. Since male guppies are known to attempt matings with other poeciliid females, we asked whether persistent courtship is also directed towards morphologically similar but phylogenetically distant females encountered following invasion. Skiffia bilineata is one of several endangered viviparous goodeids from Central México, whose remaining habitats are increasingly shared with invasive guppies. Experiments in which guppy sex ratios were manipulated to vary the proportion of heterospecific to conspecific females showed that male guppies courted and attempted forced copulations with S. bilineata females even when females of their own species were in excess. This behaviour places an additional, and previously unrecognized, burden on a group of endemic Mexican fishes already in risk of extinction.

Safety in numbers? Shoaling behaviour of the Amazonian red-bellied piranha.

Red-bellied piranha (Pygocentrus nattereri) shoals have a fearsome reputation. However, the variety and abundance of piranha predators in the flooded forests of the Amazon in which they live indicate that an important reason for shoal formation may be predator defence. Experiments using wild-caught piranhas supported the hypothesis that individual perception of risk, as revealed by elevated ventilatory frequency (opercular rate), is greater in small shoals. Moreover, exposure to a simulated predator attack by a model cormorant demonstrated that resting opercular rates are regained more quickly by piranhas in shoals of eight than they are in shoals of two. Together, these results show that shoaling has a cover-seeking function in this species.

Uncoupling the links between male mating tactics and female attractiveness

Because not all females are equally attractive, and because mating reduces the chances of getting further copulations, males should prefer better-quality mates. In this paper, we use the Trinidadian guppy (Poecilia reticulata) to explore the effects of two non-correlated measures of female quality--size and reproductive status--on male mating decisions. All male guppies employ two alternative mating tactics. We found that large females, particularly those from a high predation site, were the target of most sneaky mating attempts. The response persisted in fish raised under standard conditions over several generations in the laboratory. In addition, non-pregnant females received more courtship displays. We conclude that males can discriminate among females and that they uncouple their mating tactics to track different axes of quality.

Molecular phylogeny of the livebearing Goodeidae (Cyprinodontiformes).

The Goodeinae is a speciose group of viviparous freshwater fishes endemic to the Mesa Central of Mexico. The current taxonomy of the group is based on morphology associated with viviparity and several of the groupings are questionable. We sequenced part of the mitochondrial cytochrome c oxidase subunit I (COI) gene (627bp) and control region (approximately 430bp aligned) of representatives of 36 species (all genera) of goodeid fishes in order to establish phylogenetic relationships among the taxa. Findings support the monophyly of the Goodeidae, the sister-group relationship of the Empetrichthyinae and Goodeinae, and the relationship of Profundulus to the Goodeidae. All goodeine genera but Xenotoca were recovered as monophyletic. Many of the higher-level relationships within the group contradict the findings of previous studies based upon morphology. The rate of molecular change in COI (0.9% per Myr), calibrated with the fossil record and geological data, suggests an approximate age for the Goodeidae of 16.5Myr. The majority of divergence within the Goodeinae appears to have occurred during the Miocene, with subsequent cladogenesis in the Pliocene and Pleistocene. Most recent speciation appears allopatric. River piracy, particularly involving the Rio Ameca basin, has played a significant role in the diversification of the Goodeinae.

Uncoupling the links between male mating tactics and female attractiveness.

Because not all females are equally attractive, and because mating reduces the chances of getting further copulations, males should prefer better-quality mates. In this paper, we use the Trinidadian guppy (Poecilia reticulata) to explore the effects of two non-correlated measures of female quality--size and reproductive status--on male mating decisions. All male guppies employ two alternative mating tactics. We found that large females, particularly those from a high predation site, were the target of most sneaky mating attempts. The response persisted in fish raised under standard conditions over several generations in the laboratory. In addition, non-pregnant females received more courtship displays. We conclude that males can discriminate among females and that they uncouple their mating tactics to track different axes of quality.

Patterns of sperm precedence and predictors of paternity in the Trinidadian guppy

Despite its widespread occurrence in animals, sperm competition has been studied in a limited range of taxa. Among the most neglected groups in this respect are internally fertilizing fish in which virtually nothing is known about the dynamics of sperm competition. In this study, we examined the outcome of sperm competition when virgin female guppies mated with two males. Behavioural cues were used to ensure that each male mated once (with female cooperation) and that sperm were successfully inseminated at copulation. Two polymorphic microsatellite loci were used to estimate the proportion of offspring sired by the second male (P2) and the results revealed a bimodal distribution with either first or (more often) second male priority The observed P2 distribution differed from that expected under the 'fair raffle' model of sperm competition. Random sperm mixing is therefore unlikely to account for the observed variance in P2 in this study. A further aim of our study was to identify predictors of male reproductive success. Using logistic linear modelling, we found that the best predictors of paternity were time to remating and the difference in courtship display rate between first and second males. Males that mated quickly and performed relatively high numbers of sigmoid displays obtained greater parentage than their slower and less vigorous counterparts. Since females are attracted to high-displaying males, our results suggest that female choice may facilitate sperm competition and/or sperm choice in guppies.