A decade-long study demonstrates that a population of invasive sea lamprey (Petromyzon marinus) can be controlled by introducing sterilized males.

The release of sterilized insects to control pest populations has been used successfully during the past 6 decades, but application of the method in vertebrates has largely been overlooked or met with failure. Here, we demonstrate for the first time in fish, that a small population of sea lamprey (Petromyzon marinus; Class Agnatha), arguably one of the most impactful invasive fish in the world, can be controlled by the release of sterilized males. Specifically, the release of high numbers of sterile males (~ 1000's) into a geographically isolated population of adult sea lamprey resulted in the first multiyear delay in pesticide treatment since treatments began during 1966. Estimates of percent reduction in recruitment of age-1 sea lamprey due to sterile male release ranged from 7 to 99.9% with the precision of the estimate being low because of substantial year-to-year variability in larval density and distribution. Additional monitoring that accounts for recruitment variability in time and space would reduce uncertainty in the degree to which sterile male release reduces recruitment rates. The results are relevant to vertebrate pest control programs worldwide, especially as technical opportunities to sterilize vertebrates and manipulate sex ratios expand.

Protocol for monitoring and analyzing pheromone-mediated behavioral response of sea lamprey in a natural system.

Olfactory-mediated behaviors in fish are often examined in artificial microcosms that enable well-controlled treatments but fail to replicate environmental and social contexts. However, observing these behaviors in nature poses challenges. Here, we describe a protocol for recording sea lamprey (Petromyzon marinus) behaviors in a natural system. We describe steps for administering and verifying accurate odorant concentrations, surveying sea lamprey abundance, and tracking sea lamprey movements. We also detail procedures to analyze treatment effects on pheromone-mediated spawning in a high-density population. For complete details on the use and execution of this protocol, please refer to Scott et al.1.

Male lake char release taurocholic acid as part of a mating pheromone.

The evolutionary origins of sexual preferences for chemical signals remain poorly understood, due, in part, to scant information on the molecules involved. In the current study, we identified a male pheromone in lake char (Salvelinus namaycush) to evaluate the hypothesis that it exploits a non-sexual preference for juvenile odour. In anadromous char species, the odour of stream-resident juveniles guides migratory adults into spawning streams. Lake char are also attracted to juvenile odour but have lost the anadromous phenotype and spawn on nearshore reefs, where juvenile odour does not persist long enough to act as a cue for spawning site selection by adults. Previous behavioural data raised the possibility that males release a pheromone that includes components of juvenile odour. Using metabolomics, we found that the most abundant molecule released by males was also released by juveniles but not females. Tandem mass spectrometry and nuclear magnetic resonance were used to identify the molecule as taurocholic acid (TCA), which was previously implicated as a component of juvenile odour. Additional chemical analyses revealed that males release TCA at high rates via their urine during the spawning season. Finally, picomolar concentrations of TCA attracted pre-spawning and spawning females but not males. Taken together, our results indicate that male lake char release TCA as a mating pheromone and support the hypothesis that the pheromone is a partial match of juvenile odour.

Synergistic behavioral antagonists of a sex pheromone reduce reproduction of invasive sea lamprey.

Sex pheromones impart maximal attraction when their components are present at optimal ratios that confer balanced olfactory inputs in potential mates. Altering ratios or adding pheromone analogs to optimal mixtures may disrupt balanced olfactory antagonism and result in reduced attraction, however, tests in natural populations are lacking. We tested this hypothesis in sea lamprey (Petromyzon marinus), a fish whose male sex pheromone attracts females when two critical components, 3-keto petromyzonol sulfate (3kPZS) and petromyzonol sulfate (PZS), are present at certain ratios. Here, we report a pheromone analog, petromyzonol tetrasulfate (3sPZS), reduced female attraction to 3kPZS but not to PZS. 3sPZS mixed with additional PZS synergistically disrupted female attraction to the male pheromone and reduced spawning by 97% in a high-density population. Our results provide evidence of balanced olfactory antagonism in a vertebrate and establish a tactic to disrupt spawning of sea lamprey, a destructive invader of the Laurentian Great Lakes.

Evaluating the utility of effective breeding size estimates for monitoring sea lamprey spawning abundance.

Sea lamprey (Petromyzon marinus) is an invasive species that is a significant source of mortality for populations of valued fish species across the North American Great Lakes. Large annual control programs are needed to reduce the species' impacts; however, the number of successfully spawning adults cannot currently be accurately assessed. In this study, effective breeding size (N b) and the minimum number of spawning adults (N s) were estimated for larval cohorts from 17 tributaries across all five Great Lakes using single nucleotide polymorphisms (SNP) genotyped via RAD-capture sequencing. Reconstructed larval pedigrees showed substantial variability in the size and number of full- and half-sibling groups, N b (<1-367), and N s (5-545) among streams. Generalized linear models examining the effects of stream environmental characteristics and aspects of sampling regimes on N b and N s estimates identified sample size, the number of sampling sites, and drainage area as important factors predicting N b and N s. Correlations between N b, N s, and capture-mark-recapture estimates of adult census size (N c) increased when streams with small sample sizes (n < 50) were removed. Results collectively indicate that parameters estimated from genetic data can provide valuable information on spawning adults in a river system, especially if sampling regimes are standardized and physical stream covariates are included.

Technical Note: A procedure to place urinary catheters in 1- and 6-week-old preweaned Holstein heifer calves for the in vivo evaluation of intestinal permeability.

Oral administration of indigestible markers and subsequent urine collection is a useful method to determine in vivo gastrointestinal tract (GIT) permeability in cattle for research purposes. However, urine sampling techniques often rely on total waste collection, which reduces the ability to perform more frequent sampling and obtain accurate volumes and sterile samples. An alternative is urethral catheterization, though the feasibility of this technique has not been thoroughly tested in preweaned Holstein heifer calves. The study objective was to develop a urethral catheter placement procedure in preweaned Holstein heifer calves for continuous and accurate urine collection to evaluate GIT permeability using an indigestible marker. Fifteen Holstein heifer calves had catheters placed at approximately 1 wk (8.0 ± 1.5 d) and 6 wk (40.0 ± 1.5 d) of age. During the procedure, calves were individually housed and restrained. The vulva was sterilized and then a sterile, lubricated speculum was inserted into the vagina. A sterile 0.09 cm diameter guidewire was guided into a lubricated, sterile 10 French Foley catheter. The catheter was inserted at approximately 5 through 7 cm into the urethral opening, guided into the bladder, and the catheter balloon was filled with 10 mL of water. The guidewire was removed, and urine flow confirmed correct placement before a 4-L urinary drainage bag was attached to the catheter. After catheterization (24 h), 1 L of chromium (Cr)-ethylenediaminetetraacetic acid was orally dosed to the calves. Calf health observations were made six times over a 48-h period, and any occurrence of vaginal discharge, tissue discharge in catheter, bleeding, inflammation, or abnormal urine was considered a localized reaction. The proportion of localized reactions for each age group was determined using Microsoft Excel, and the total Cr output was analyzed using PROC GLIMMIX. Localized reactions occurred for 20.0% of the 1-wk-old calves and 13.3% of the 6-wk-old calves. In the first 4 h, urine was collected every 15 min, and there were no overall Cr output differences (P = 0.38; 10.28 ± 3.21 mg Cr) when comparing 1- and 6-wk-old calves. However, 1-wk-old calves tended (P = 0.08) to have greater overall Cr output at 480 min (19.2%) and 1,440 min (41.9%) when compared with 6-wk-old calves. In summary, urinary catheterization is a viable urinary collection method for the determination of in vivo GIT permeability in preweaned Holstein heifer calves.

Neonatal calves are highly susceptible to enteric disease during their first few weeks of life, and enteric disease is the leading cause of preweaning morbidity and mortality. A consequence of enteric disease is greater gastrointestinal tract (GIT) permeability in neonatal calves, which is also influenced by reduced intestinal maturity and environmental factors. Therefore, an accurate and precise method of evaluating GIT permeability in neonatal calves is necessary to develop appropriate treatment and mitigation strategies. The oral administration of indigestible markers and measurement of their presence in urine is an accepted method to determine the total GIT permeability in mature heifers. However, current urine collection methods in preweaned heifer calves may not be reliable. Therefore, the study objective was to develop a urinary catheterization method to collect urine accurately and precisely for the in vivo determination of GIT permeability in 1- and 6-wk-old Holstein heifer calves. It was determined that the urinary catheterization procedure and collection system developed in this study were viable and could be applied when evaluating GIT permeability in preweaned Holstein heifer calves using orally dosed indigestible markers.

Pedigree analysis and estimates of effective breeding size characterize sea lamprey reproductive biology.

The sea lamprey (Petromyzon marinus) is an invasive species in the Great Lakes and the focus of a large control and assessment program. Current assessment methods provide information on the census size of spawning adult sea lamprey in a small number of streams, but information characterizing reproductive success of spawning adults is rarely available. We used RAD-capture sequencing to genotype single nucleotide polymorphism (SNP) loci for ~1600 sea lamprey larvae collected from three streams in northern Michigan (Black Mallard, Pigeon, and Ocqueoc Rivers). Larval genotypes were used to reconstruct family pedigrees, which were combined with Gaussian mixture analyses to identify larval age classes for estimation of spawning population size. Two complementary estimates of effective breeding size (N b), as well as the extrapolated minimum number of spawners (N s), were also generated for each cohort. Reconstructed pedigrees highlighted inaccuracies of cohort assignments from traditionally used mixture analyses. However, combining genotype-based pedigree information with length-at-age assignment of cohort membership greatly improved cohort identification accuracy. Population estimates across all three streams sampled in this study indicate a small number of successfully spawning adults when barriers were in operation, implying that barriers limited adult spawning numbers but were not completely effective at blocking access to spawning habitats. Thus, the large numbers of larvae present in sampled systems were a poor indicator of spawning adult abundance. Overall, pedigree-based N b and N s estimates provide a promising and rapid assessment tool for sea lamprey and other species.

Corrigendum: Gut Microbiota Associated With Different Sea Lamprey (Petromyzon marinus) Life Stages.

[This corrects the article DOI: 10.3389/fmicb.2021.706683.].

Gut Microbiota Associated With Different Sea Lamprey (Petromyzon marinus) Life Stages.

Sea lamprey (SL; Petromyzon marinus), one of the oldest living vertebrates, have a complex metamorphic life cycle. Following hatching, SL transition into a microphagous, sediment burrowing larval stage, and after 2-10+ years, the larvae undergo a dramatic metamorphosis, transforming into parasitic juveniles that feed on blood and bodily fluids of fishes; adult lamprey cease feeding, spawn, and die. Since gut microbiota are critical for the overall health of all animals, we examined the microbiota associated with SLs in each life history stage. We show that there were significant differences in the gut bacterial communities associated with the larval, parasitic juvenile, and adult life stages. The transition from larval to the parasitic juvenile stage was marked with a significant shift in bacterial community structure and reduction in alpha diversity. The most abundant SL-associated phyla were Proteobacteria, Fusobacteria, Bacteroidetes, Verrucomicrobia, Actinobacteria, and Firmicutes, with their relative abundances varying among the stages. Moreover, while larval SL were enriched with unclassified Fusobacteriaceae, unclassified Verrucomicrobiales and Cetobacterium, members of the genera with fastidious nutritional requirements, such as Streptococcus, Haemophilus, Cutibacterium, Veillonella, and Massilia, were three to four orders of magnitude greater in juveniles than in larvae. In contrast, adult SLs were enriched with Aeromonas, Iodobacter, Shewanella, and Flavobacterium. Collectively, our findings show that bacterial communities in the SL gut are dramatically different among its life stages. Understanding how these communities change over time within and among SL life stages may shed more light on the role that these gut microbes play in host growth and fitness.

Diel Patterns of Pheromone Release by Male Sea Lamprey.

Costs to producing sexual signals can create selective pressures on males to invest signaling effort in particular contexts. When the benefits of signaling vary consistently across time, males can optimize signal investment to specific temporal contexts using biological rhythms. Sea lamprey, Petromyzon marinus, have a semelparous life history, are primarily nocturnal, and rely on pheromone communication for reproduction; however, whether male investment in pheromone transport and release matches increases in spawning activity remains unknown. By measuring (1) 3keto-petromyzonol sulfate (3kPZS, a main pheromone component) and its biosynthetic precursor PZS in holding water and tissue samples at six points over the course of 24 hours and (2) 3kPZS release over the course of several days, we demonstrate that 3kPZS release exhibits a consistent diel pattern across several days with elevated pheromone release just prior to sunset and at night. Trends in hepatic concentrations and circulatory transport of PZS and 3kPZS were relatively consistent with patterns of 3kPZS release and suggest the possibility of direct upregulation in pheromone transport and release rather than observed release patterns being solely a byproduct of increased behavioral activity. Our results suggest males evolved a signaling strategy that synchronizes elevated pheromone release with nocturnal increases in sea lamprey behavior. This may be imperative to ensure that male signaling effort is not wasted in a species having a single, reproductive event.

Exploiting common senses: sensory ecology meets wildlife conservation and management.

Multidisciplinary approaches to conservation and wildlife management are often effective in addressing complex, multi-factor problems. Emerging fields such as conservation physiology and conservation behaviour can provide innovative solutions and management strategies for target species and systems. Sensory ecology combines the study of 'how animals acquire' and process sensory stimuli from their environments, and the ecological and evolutionary significance of 'how animals respond' to this information. We review the benefits that sensory ecology can bring to wildlife conservation and management by discussing case studies across major taxa and sensory modalities. Conservation practices informed by a sensory ecology approach include the amelioration of sensory traps, control of invasive species, reduction of human-wildlife conflicts and relocation and establishment of new populations of endangered species. We illustrate that sensory ecology can facilitate the understanding of mechanistic ecological and physiological explanations underlying particular conservation issues and also can help develop innovative solutions to ameliorate conservation problems.

Behavioural responses of female lake trout Salvelinus namaycush to male chemical stimuli and prostaglandin F2α.

Male olfactory cues may guide aggregation on spawning reefs, mate evaluation and synchronized gamete release in lake trout Salvelinus namaycush, but a lack of information on the source and identity of the cues precludes direct tests of their function. Using a two-channel flume, we found ovulated female lake trout increased time spent in the channel treated with spermiated male-conditioned water, urine and bile but not synthesized prostaglandin F2α . We suggest future efforts to characterize male olfactory cues focus on urine and postulate that bile acids contribute to its behavioural activity.

A pheromone antagonist liberates female sea lamprey from a sensory trap to enable reliable communication.

The evolution of male signals and female preferences remains a central question in the study of animal communication. The sensory trap model suggests males evolve signals that mimic cues used in nonsexual contexts and thus manipulate female behavior to generate mating opportunities. Much evidence supports the sensory trap model, but how females glean reliable information from both mimetic signals and their model cues remains unknown. We discovered a mechanism whereby a manipulative male signal guides reliable communication in sea lamprey (Petromyzon marinus). Migratory sea lamprey follow a larval cue into spawning streams; once sexually mature, males release a pheromone that mimics the larval cue and attracts females. Females conceivably benefit from the mimetic pheromone during mate search but must discriminate against the model cue to avoid orienting toward larvae in nearby nursery habitats. We tested the hypothesis that spawning females respond to petromyzonol sulfate (PZS) as a behavioral antagonist to avoid attraction to the larval cue while tracking the male pheromone despite each containing attractive 3-keto petromyzonol sulfate (3kPZS). We found 1) PZS inhibited electrophysiological responses to 3kPZS and abated preferences for 3kPZS when mixed at the same or greater concentrations, 2) larvae released more PZS than 3kPZS whereas males released more 3kPZS than PZS, and 3) mixtures of 3kPZS and PZS applied at ratios measured in larval and male odorants resulted in the discrimination observed between the natural odors. Our study elucidates how communication systems that arise via deception can facilitate reliable communication.

Behavioral Responses of Sea Lamprey to Varying Application Rates of a Synthesized Pheromone in Diverse Trapping Scenarios.

Use of the first fish pheromone biopesticide, 3-keto petromyzonol sulfate (3kPZS) in sea lamprey (Petromyzon marinus) control requires an understanding of both how the amount 3kPZS applied to a trap relates to catch, and how that relationship varies among stream types. By conducting 3kPZS dose-response experiments over two years and across six varied trapping contexts, we conclude (1) that 3kPZS application is best standardized by how much is emitted from the trap instead of the fully mixed concentration achieved downstream, and (2) that 3kPZS is more effective in wide streams (>30 m). In wide streams, emission of 3kPZS at 50 mg hr.-1 from the trap increased capture rate by 10-15% as sea lamprey were 25-50% more likely to enter the trap after encounter. However, in narrow streams (< 15 m), 50 mg hr.-1 3kPZS generally reduced probabilities of upstream movement, trap encounter, and entrance. While 3kPZS significantly influenced upstream movement, encounter, and capture probabilities, these behaviors were also highly influenced by water temperature, stream width, sea lamprey length, and sex. This study highlights that a pheromone component in a stream environment does not ubiquitously increase trap catch in all contexts, but that where, how, and when the pheromone is applied has major impacts on whether it benefits or hinders trapping efforts.

Intra- and Interspecific Variation in Production of Bile Acids That Act as Sex Pheromones in Lampreys.

Pheromones are important sexual signals in most animals, but research into their evolution is largely biased toward insects. Lampreys are a jawless fish with a relatively well-understood pheromone communication system, and they offer a useful opportunity to study pheromone evolution in a vertebrate. Once sexually mature, male sea lamprey (Petromyzon marinus) and likely other lampreys produce and release bile acids that act as sex pheromones. Spawning males do not feed and therefore produce bile acids primarily for sexual communication, whereas larvae produce the same bile acids but for digestion, offering an opportunity to compare the evolution of bile acids produced for sexual versus nonsexual functions. We profiled eight pheromone-related bile acids in livers from larvae and males and determined the effect of life stage on intra- and interspecific variation in bile acid production. Our results indicate less variation among males than larvae within P. marinus but more variation among species for males than larvae. We postulate that bile acid production in males is shaped by directional or stabilizing selection that reduces variance within P. marinus and directional or disruptive selection that promotes diversification across species. Although our results offer support for the role of sexual selection in the evolution of lamprey pheromones, they do not eliminate possible roles of other aspects of lamprey ecology.

Dreissenid (quagga and zebra mussel) veligers are adversely affected by bloom forming cyanobacteria.

Quagga (Dreissena rostriformis bugensis) and zebra (D. polymorpha) mussels are broadcast spawners that produce planktonic, free swimming veligers, a life history strategy dissimilar to native North American freshwater bivalves. Dreissenid veligers require highly nutritious food to grow and survive, and thus may be susceptible to increased mortality rates during harsh environmental conditions like cyanobacteria blooms. However, the impact of cyanobacteria and one of the toxins they can produce (microcystin) has not been evaluated in dreissenid veligers. Therefore, we exposed dreissenid veligers to eleven distinct cultures (isolates) of cyanobacteria representing Anabaena, Aphanizomenon, Dolichospermum, Microcystis, and Planktothrix species and the cyanotoxin microcystin to determine the lethality of cyanobacteria on dreissenid veligers. Six-day laboratory bioassays were performed in microplates using dreissenid veligers collected from the Detroit River, Michigan, USA. Veligers were exposed to increasing concentrations of cyanobacteria and microcystin using the green algae Chlorella minutissima as a control. Based on dose response curves formulated from a Probit model, the LC50 values for cyanobacteria used in this study range between 15.06 and 135.06 µg/L chlorophyll-a, with the LC50 for microcystin-LR at 13.03 µg/L. Because LC50 values were within ranges observed in natural waterbodies, it is possible that dreissenid recruitment may be suppressed when veliger abundances overlap with seasonal cyanobacteria blooms. Thus, the toxicity of cyanobacteria to dreissenid veligers may be useful to include in models forecasting dreissenid mussel abundance and spread.

Is there convergence of gut microbes in blood-feeding vertebrates?

Animal microbiomes play an important role in dietary adaptation, yet the extent to which microbiome changes exhibit parallel evolution is unclear. Of particular interest is an adaptation to extreme diets, such as blood, which poses special challenges in its content of proteins and lack of essential nutrients. In this study, we assessed taxonomic signatures (by 16S rRNA amplicon profiling) and potential functional signatures (inferred by Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt)) of haematophagy in birds and bats. Our goal was to test three alternative hypotheses: no convergence of microbiomes, convergence in taxonomy and convergence in function. We find a statistically significant effect of haematophagy in terms of microbial taxonomic convergence across the blood-feeding bats and birds, although this effect is small compared to the differences found between haematophagous and non-haematophagous species within the two host clades. We also find some evidence of convergence at the predicted functional level, although it is possible that the lack of metagenomic data and the poor representation of microbial lineages adapted to haematophagy in genome databases limit the power of this approach. The results provide a paradigm for exploring convergent microbiome evolution replicated with independent contrasts in different host lineages. This article is part of the theme issue 'Convergent evolution in the genomics era: new insights and directions'.

Cyanobacteria reduce motility of quagga mussel (Dreissena rostriformis bugensis) sperm.

The temporal expansion of harmful algal blooms, primarily associated with cyanobacteria, may impact aquatic organisms at vulnerable life-history stages. Broadcast spawning species release gametes into the water column for external fertilization, directly exposing sperm to potential aquatic stressors. To determine if cyanobacteria can disrupt reproduction in freshwater broadcast spawners, we evaluated sublethal effects of cyanobacteria exposure on quagga mussel (Dreissena rostriformis bugensis) sperm. In laboratory studies, sperm were collected after inducing mussels to spawn using serotonin and exposed to 11 cultures of cyanobacteria including Anabaena flos-aquae, Aphanizomenon flos-aquae, Dolichospermum lemmermannii, Gloeotrichia echinulata, 5 cultures of Microcystis aeruginosa, M. wesenbergii, and Planktothrix suspensa. Sperm motility, using endpoints of cumulative distance traveled and mean velocity, was calculated for a minimum of 10 individual sperm using a novel optical biotracking assay method. The distance and velocity at which sperm traveled decreased when exposed to Aphanizomenon flos-aquae and 2 M. aeruginosa cultures. Our findings indicate that cyanobacteria impede the motility of quagga mussel sperm, which can potentially result in reproductive impairments to mussels and potentially other broadcast spawning species. Environ Toxicol Chem 2019;38:368-374. © 2018 SETAC.

Push and pull of downstream moving juvenile sea lamprey (Petromyzon marinus) exposed to chemosensory and light cues.

Visual and olfactory stimuli induce behavioural responses in fishes when applied independently, but little is known about how simultaneous exposure influences behaviour, especially in downstream migrating fishes. Here, downstream moving juvenile sea lamprey (Petromyzon marinus) were exposed to light and a conspecific chemosensory alarm cue in a flume and movement were monitored with overhead cameras and nets. When exposed to light, sea lamprey were more likely to be captured in a net closest to the light array. When exposed to the alarm cue, sea lamprey transit rate through the flume increased, but sea lamprey did not avoid the alarm cue plume by moving perpendicular to flow. When the alarm cue and light were applied simultaneously in a push and pull configuration, the alarm cue still triggered enhanced downstream movement (push downstream) and more sea lamprey was still captured in the net nearest the light (pull to the side), resulting in twice as many sea lamprey being captured in the lighted net relative to controls. To our knowledge, this is the first study using multiple sensory cues in a push-pull configuration to modulate fish outmigration. Push and pull of juvenile sea lamprey with sensory cues could be useful to reduce turbine entrainment where native and enhance trap catch where invasive.