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Open Access Publications from the University of California

Scholarly Works (10 results)

  • Article
Coastal Environmental Quality Initiative (2004)

Southern California has historically supported 5 species of commercial abalone. Within the past fifteen years, all of these species have seen dramatic declines in population. Now, abalones occur at such low population densities that in 1996 the California Fish and Game Commission was forced to order an emergency closure to all abalone harvesting in southern California. For abalones, fertilization takes place externally after males and females spawn their gametes into the water column. Currently, the numbers of mature adults are so low that fertilization may be a critical bottleneck for population recovery. In this proposal, we seek to determine the effects of population size and distribution, and hydrodynamic conditions on fertilization success. This will be accomplished through three phases of this project: (i) through abalone cruises sponsored by the California Department of Fish and Game, we will take flow measurements and determine the population densities and distributions of naturally occurring abalone populations in the Channel Islands, (ii) measurements, taken at sites that have historically supported large populations of abalone, will allow us to scale our laboratory flume experiments to examine the effects of fluid motion on the transport and mixing of gametes, and (iii) we will determine the necessary number and spacing of spawning abalones for successful fertilization, under conditions similar to those in the field. The first phase of this project will bring critical information on the current abalone population demogrpahics, and allow us to scale our laboratory experiments. The second and third phase of this project will allow predictions to be made on the minimum population size necessary for successful fertilization, and the influence of fluid motion and habitat on fertilization. Such information will be critical for marine resource managers to establish proper procedures to aid in the recovery of the remaining abalone populations in southern California.

    Cover page: Fertilization in the sea: Establishing the minimum population sizes and environmental conditions for successful fertilization in abalone
    • Article
    Research Theses and Dissertations (2004)

    Chemical communication between sperm and eggs is ubiquitous in organisms with widely divergent reproductive strategies. Sperm attractants are found in marine taxa that broadcast their gametes into the sea, as well as terrestrial organisms with internal fertilization, such as humans. Chemosensory-mediated behavior thus is a key component in sperm-egg interactions and fertilization. Despite nearly a century of research, the mechanisms controlling fertilization remains one of the least understood biological processes. For example, waterborne egg-factors that attract sperm are thought to be ecologically meaningful for increasing gamete encounters, or evolutionary significant by maintaining species barriers, but the contributions remains unknown. In this study, I (i) developed analytical and behavioral techniques to establish the reproductive consequences of sperm attractants, and (ii) examined the biological processes controlling fertilization success in the red abalone, Haliotis rufescens. Using RP and size-exclusion chromatographic teclmiques, the amino acid L-tryptophan, was found to be the natural sperm attractant. The production of tryptophan from live abalone eggs elicited sperm chemotaxis, effectively doubling the egg size. When the enzyme tryptophanase, which selectively degrades tryptophan, was added to the seawater around eggs, sperm no longer were able to locate the eggs, gamete encounters dropped, and fertilization levels dramatically lowered. Thus, the natural tryptophan gradient is critical for gamete encounters. To establish the evolutionary consequences of sperm attractants, red and green (Haliotis fulgens) abalone gametes were crossed, and fertilization assays conducted. Although long theorized as baniers to hybridization, species-specific sperm attractants were only minor contributors to reproductive isolation. When the influence of sperm and egg concentration, sperm-to-egg ratio, and gamete contact times on reproductive success was established, egg concentration had the same effect as sperm concentration on fertilization rates, and eggs, not sperm, were the limiting factor controlling abalone fecundity. These results contrast widely with the theory that sperm is the primary determinant for fe1iilization success. Given the fact that eggs, rather then sperm, effectively control reproduction, chemoattractants may have evolved thru sperm competition.

     

     

      Cover page: Establishing the Biological and Chemical Processes Regulating Fertilization Success in the Red Abalone, Haliotis rufescens
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2022)
      Female mosquitoes use chemical and physical cues, including vision, smell, heat, and humidity, to orient toward hosts. Body odors are produced by skin resident bacteria that convert metabolites secreted in sweat into odorants that confer the characteristic body scent. Mosquitoes detect these compounds using olfactory receptors in their antennal olfactory receptor neurons. Such information is further integrated with the senses of temperature and humidity, as well as vision, processed in the brain into a behavioral output, leading to host finding. Knowledge of human scent components unveils a variety of odorants that are attractive to mosquitoes, but also odor-triggering repellency. Finding ways to divert human-seeking behavior by female mosquitoes using odorants can possibly mitigate mosquito-borne pathogen transmission.
        Cover page: Human attractive cues and mosquito host-seeking behavior.
        • Article
        • Peer Reviewed
        UC Santa Barbara Previously Published Works (2022)
        Mosquitoes track odors, locate hosts, and find mates visually. The color of a food resource, such as a flower or warm-blooded host, can be dominated by long wavelengths of the visible light spectrum (green to red for humans) and is likely important for object recognition and localization. However, little is known about the hues that attract mosquitoes or how odor affects mosquito visual search behaviors. We use a real-time 3D tracking system and wind tunnel that allows careful control of the olfactory and visual environment to quantify the behavior of more than 1.3 million mosquito trajectories. We find that CO2 induces a strong attraction to specific spectral bands, including those that humans perceive as cyan, orange, and red. Sensitivity to orange and red correlates with mosquitoes' strong attraction to the color spectrum of human skin, which is dominated by these wavelengths. The attraction is eliminated by filtering the orange and red bands from the skin color spectrum and by introducing mutations targeting specific long-wavelength opsins or CO2 detection. Collectively, our results show that odor is critical for mosquitoes' wavelength preferences and that the mosquito visual system is a promising target for inhibiting their attraction to human hosts.
          Cover page: The olfactory gating of visual preferences to human skin and visible spectra in mosquitoes
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2021)
          Blood-feeding insects, such as the mosquito, Aedes (Ae.) aegypti, use multiple senses to seek out and bite humans.1,2 Upon exposure to the odor of CO2, the attention of female mosquitoes to potential targets is greatly increased. Female mosquitoes are attracted to high-contrast visual cues and use skin olfactory cues to assist them in homing in on targets several meters away.3-9 Within close range, convective heat from skin and additional skin odors further assist the mosquitoes' evaluation as to whether the object of interest might be a host.10,11 Here, using CRISPR-Cas9, we mutated the gene encoding Op1, which is the most abundant of the five rhodopsins expressed in the eyes of Ae. aegypti. Using cage and wind-tunnel assays, we found that elimination of op1 did not impair CO2-induced target seeking. We then mutated op2, which encodes the rhodopsin most similar to Op1, and also found that there was no impact on this behavior. Rather, mutation of both op1 and op2 was required for abolishing vision-guided target attraction. In contrast, the double mutants exhibited normal phototaxis and odor-tracking responses. By measuring the walking optomotor response, we found that the double mutants still perceived optic flow. In further support of the conclusion that the double mutant is not blind, the animals retained an electrophysiological response to light, although it was diminished. This represents the first genetic perturbation of vision in mosquitoes and indicates that vision-guided target attraction by Ae. aegypti depends on two highly related rhodopsins.
            Cover page: Elimination of vision-guided target attraction in Aedes aegypti using CRISPRCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2020)
            Mosquitoes are important vectors of disease and require sources of carbohydrates for reproduction and survival. Unlike host-related behaviors of mosquitoes, comparatively less is understood about the mechanisms involved in nectar-feeding decisions, or how this sensory information is processed in the mosquito brain. Here we show that Aedes spp. mosquitoes, including Aedes aegypti, are effective pollinators of the Platanthera obtusata orchid, and demonstrate this mutualism is mediated by the orchid's scent and the balance of excitation and inhibition in the mosquito's antennal lobe (AL). The P. obtusata orchid emits an attractive, nonanal-rich scent, whereas related Platanthera species-not visited by mosquitoes-emit scents dominated by lilac aldehyde. Calcium imaging experiments in the mosquito AL revealed that nonanal and lilac aldehyde each respectively activate the LC2 and AM2 glomerulus, and remarkably, the AM2 glomerulus is also sensitive to N,N-diethyl-meta-toluamide (DEET), a mosquito repellent. Lateral inhibition between these 2 glomeruli reflects the level of attraction to the orchid scents. Whereas the enriched nonanal scent of P. obtusata activates the LC2 and suppresses AM2, the high level of lilac aldehyde in the other orchid scents inverts this pattern of glomerular activity, and behavioral attraction is lost. These results demonstrate the ecological importance of mosquitoes beyond operating as disease vectors and open the door toward understanding the neural basis of mosquito nectar-seeking behaviors.
              Cover page: The olfactory basis of orchid pollination by mosquitoes
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (2018)
              How mosquitoes determine which individuals to bite has important epidemiological consequences. This choice is not random; most mosquitoes specialize in one or a few vertebrate host species, and some individuals in a host population are preferred over others. Mosquitoes will also blood feed from other hosts when their preferred is no longer abundant, but the mechanisms mediating these shifts between hosts, and preferences for certain individuals within a host species, remain unclear. Here, we show that olfactory learning may contribute to Aedes aegypti mosquito biting preferences and host shifts. Training and testing to scents of humans and other host species showed that mosquitoes can aversively learn the scent of specific humans and single odorants and learn to avoid the scent of rats (but not chickens). Using pharmacological interventions, RNAi, and CRISPR gene editing, we found that modification of the dopamine-1 receptor suppressed their learning abilities. We further show through combined electrophysiological and behavioral recordings from tethered flying mosquitoes that these odors evoke changes in both behavior and antennal lobe (AL) neuronal responses and that dopamine strongly modulates odor-evoked responses in AL neurons. Not only do these results provide direct experimental evidence that olfactory learning in mosquitoes can play an epidemiological role, but collectively, they also provide neuroanatomical and functional demonstration of the role of dopamine in mediating this learning-induced plasticity, for the first time in a disease vector insect.
                Cover page: Modulation of Host Learning in Aedes aegypti Mosquitoes
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2019)

                Background

                The mosquito Aedes aegypti has a wide variety of sensory pathways that have supported its success as a species as well as a highly competent vector of numerous debilitating infectious pathogens. Investigations into mosquito sensory systems and their effects on behavior are valuable resources for the advancement of mosquito control strategies. Numerous studies have elucidated key aspects of mosquito sensory systems, however there remains critical gaps within the field. In particular, compared to that of the adult form, there has been a lack of studies directed towards the immature life stages. Additionally, although numerous studies have pinpointed specific sensory receptors as well as responding motor outputs, there has been a lack of studies able to monitor both concurrently.

                Results

                To begin filling aforementioned gaps, here we engineered Ae. aegypti to ubiquitously express a genetically encoded calcium indicator, GCaMP6s. Using this strain, combined with advanced microscopy, we simultaneously measured live stimulus-evoked calcium responses in both neuronal and muscle cells with a wide spatial range and resolution.

                Conclusions

                By coupling in vivo live calcium imaging with behavioral assays we were able to gain functional insights into how stimulus-evoked neural and muscle activities are represented, modulated, and transformed in mosquito larvae enabling us to elucidate mosquito sensorimotor properties important for life-history-specific foraging strategies.
                  Cover page: Live calcium imaging of Aedes aegypti neuronal tissues reveals differential importance of chemosensory systems for life-history-specific foraging strategies
                  • Article
                  • Peer Reviewed
                  UC Riverside Previously Published Works (2019)
                  Mosquitoes rely on the integration of multiple sensory cues, including olfactory, visual, and thermal stimuli, to detect, identify, and locate their hosts [1-4]. Although we increasingly know more about the role of chemosensory behaviors in mediating mosquito-host interactions [1], the role of visual cues is comparatively less studied [3], and how the combination of olfactory and visual information is integrated in the mosquito brain remains unknown. In the present study, we used a tethered-flight light-emitting diode (LED) arena, which allowed for quantitative control over the stimuli, and a control theoretic model to show that CO2 modulates mosquito steering responses toward vertical bars. To gain insight into the neural basis of this olfactory and visual coupling, we conducted two-photon microscopy experiments in a new GCaMP6s-expressing mosquito line. Imaging revealed that neuropil regions within the lobula exhibited strong responses to objects, such as a bar, but showed little response to a large-field motion. Approximately 20% of the lobula neuropil we imaged were modulated when CO2 preceded the presentation of a moving bar. By contrast, responses in the antennal (olfactory) lobe were not modulated by visual stimuli presented before or after an olfactory stimulus. Together, our results suggest that asymmetric coupling between these sensory systems provides enhanced steering responses to discrete objects.
                    Cover page: Visual-Olfactory Integration in the Human Disease Vector Mosquito Aedes aegypti
                    • Article
                    • Peer Reviewed
                    UC Irvine Previously Published Works (2011)
                    In the female reproductive tract, mammalian sperm undergo a regulated sequence of prefusion changes that "prime" sperm for fertilization. Among the least understood of these complex processes are the molecular mechanisms that underlie sperm guidance by environmental chemical cues. A "hard-wired" Ca(2+) signaling strategy that orchestrates specific motility patterns according to given functional requirements is an emerging concept for regulation of sperm swimming behavior. The molecular players involved, the spatiotemporal characteristics of such motility-associated Ca(2+) dynamics, and the relation between a distinct Ca(2+) signaling pattern and a behavioral sperm phenotype, however, remain largely unclear. Here, we report the functional characterization of two human sperm chemoreceptors. Using complementary molecular, physiological, and behavioral approaches, we comparatively describe sperm Ca(2+) responses to specific agonists of these novel receptors and bourgeonal, a known sperm chemoattractant. We further show that individual receptor activation induces specific Ca(2+) signaling patterns with unique spatiotemporal dynamics. These distinct Ca(2+) dynamics are correlated to a set of stimulus-specific stereotyped behavioral responses that could play vital roles during various stages of prefusion sperm-egg chemical communication.
                    • 1 supplemental PDF
                    Cover page: Chemosensory Ca2+ Dynamics Correlate with Diverse Behavioral Phenotypes in Human Sperm*Creative Commons 'BY' version 4.0 license
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