Naim M. Bautista, Ph.D.
Research
Overview: My research program is focused on dissecting the cardiovascular and respiratory mechanisms that underlie the capacity to face, cope, acclimate and adapt to challenging conditions. I am interested in elucidating the relative contribution of the genetic and non-genetic factors that underly these processes. I utilize techniques that span from the molecular to the organismal levels of organization, for conciliating the mechanisms with responses at the tissue, system, and whole-organism levels. My research is distinct because it expands upon classic within-generational studies and delves into the cross- and transgenerational dimensions. I am genuinely interested in understanding the mechanisms of inheritance and how adaptive and maladaptive traits are conserved across generations.
“If I have seen further, it is by standing on the shoulders of giants.”
(Isaac Newton)
Professional Development
Postdoc 2021-Present
University of Nebraska-Lincoln with Professor Jay F. Storz
Postdoc 2019-2021
Aarhus University with Professor Angela Fago
Doctoral studies (Ph.D.) 2015-2019
University of North Texas with Professor Warren W. Burggren
Research Projects
I. Cross-generational Responses to Environmental Stressors in Vertebrates: From Organisms to Molecules
Ever since Darwin, researchers around the world have focused their efforts on understanding how natural populations persist in challenging environmental conditions. Central to answering this question is the understanding of how parental populations (P0) influence their offspring's survivability. Environmental experiences of the parental populations may result in the offspring's acquisition of adaptive phenotypes that improve their resistance to the stressor experienced by their parents. Contrastingly, the acquisition of maladaptive phenotypes can also occur, even when the offspring themselves have not experienced the stressor. Doctoral studies were focused on understanding the effect of environmentally persistent stressors (i.e., hypoxia, crude oil) on the physiology of parental populations and their offspring. I used the zebrafish and the king quail as animal models to approach this question. Through a series of common garden studies in which I exposed parental populations of zebrafish to hypoxia and to crude oil through their diet (or their combination), I determined the effects of the exposure on: a) their physiology (i.e., heart rate, stroke volume, cardiac output); b) their breeding capacity, fecundity, and gamete quality (Fig.1A); and c) the effects of the PO exposure on their offspring survivability and physiology (Fig.1B). I compared the physiological responses of their offspring against those of F1 derived from control parents (non-exposed) when they themselves were raised in clean water or in crude oil polluted water. To determine the effects at the organ level, I performed histology and immunohistochemistry studies, as well as epigenetic analysis of DNA methylation (Fig.1C), and the expression of genes related to crude oil detoxification, cardiac development and stress, DNA methylation maintenance, and response to hypoxia. These measurements were performed in both populations. Remarkably, F1 larvae derived from oil-exposed parents, when reared in oiled water, showed a 30% enhanced survival compared with controls. Unexpectedly, F1 larvae from oil-exposed parents showed poorer survival in clean water [6]. Additionally, parental oil exposure induced bradycardia (presumably maladaptive) in F1 larvae in both clean and oiled water (Fig.1B). Furthermore, maternal, paternal, and dual parental exposure all enhanced the survival of their F1 offspring raised in oiled conditions and Compared with offspring from control parents, global DNA methylation was decreased in the three offspring groups derived from oil-exposed parents (Fig.1C) [10]. By exposing parental populations of the king quail to oil-polluted food, I determined the effects of the exposure on whole animal metabolism (Fig.1D). By employing flow-through respirometry protocols measured oxygen consumption rates (ṀO2), ventilation traits (i.e., minute ventilation, breathing frequency, tidal volume, respiratory exchange), and analyzed how hematological properties (i.e., OSM, pH, PO2, PCO2, [HCO3], HCT, MCV), varied in response to the exposure. I also measured these variables in their offspring. Notably, we found that parental exposure to crude oil increases water loss of their eggs (Fig.1E) and impacts their offspring’s thermoregulatory capacity (Fig.1F). Overall, phenotypic responses during exposure to persistent environmental stressors in F1 offspring are influenced by maternal and paternal experiences. This parent-to-offspring influence (whether genetic or epigenetic) can lead to an immediate and simultaneous inheritance of both beneficial and maladaptive traits in a large proportion of the F1 generation.
Figure 1. Parental environmental experiences influence their offspring’s physiological traits. A) A PO of zebrafish were exposed to a stressor and the effects of the exposure were investigated in their gametes and their F1 offspring. B) Heart rate of the F1 offspring is strongly affected by the parental exposure. C) These effects are correlated with changes in DNA methylation in the heart of the offspring; D) Dietary exposure to crude oil in a PO of king quail resulted in: E) increased water loss of their eggs, and F) impaired thermoregulatory capacity of their F1.
II. A unique Oxygen Transport Adaptation of Crocodilians
Figure 2. The extraordinary capacity for breath-holding in crocodilians while killing prey is facilitated by their unique allosteric regulation of hemoglobin oxygen binding by CO2 and HCO3-. A) Spectacled caiman inside a respirometer chamber to simulate diving. B) Increase in Hb bound HCO3- as diving time increases and Hb saturation decreased. C) Absorbance trace of the decrease in Hb saturation induced by changes in PCO2, obtained with a thin-layer diffusion chamber. D) Increase in O2 released from Hb1 and Hb2 upon injection of bicarbonate.
Crocodilians are able to remain submerged underwater for extraordinarily long periods of time, a physiological capacity that allows them to kill large mammalian prey like wildebeest and zebras by dragging them underwater and drowning them. This remarkable capacity for breath-holding is facilitated by the allosteric regulation of their hemoglobin oxygen binding capacity by bicarbonate (HCO3-) ions, a unique property among vertebrate hemoglobins. This bicarbonate sensitivity of crocodilian hemoglobin was first described in vitro, but the allosteric effect was inferred without direct experimental verification of bicarbonate binding to Hb. Subsequent studies on Hbs from other crocodilian species documented a direct allosteric effect of CO2, but the direct contribution of bicarbonate binding was neither confirmed in these studies nor quantified. The reason is likely that it is difficult to experimentally distinguish the allosteric effects of CO2 from those of bicarbonate and protons because at equilibrium all these three compounds are present in solution. Moreover, previous studies used different experimental and buffer conditions and rarely accounted for the potential effect of other anions, such as chloride ions, which are potent allosteric modulators of crocodilian Hb–O2 affinity. Therefore, during my postdoctoral position at Aarhus University, I performed in vivo and in vitro studies to: a) address the hypothesis that CO2 primarily binds to hemoglobin during diving in crocodilians, rather than being accumulated in plasma, as in other vertebrates; and b) to separate the allosteric effects of CO2 and bicarbonate on crocodilian Hb oxygenation by utilizing kinetic and equilibrium approaches at a constant pH and in the absence of chloride ions or organic phosphates. Our in vivo data show that the metabolically produced CO2 is largely bound as HCO3- to hemoglobin, as Hb–O2 saturation fell during the dive (Fig.2A,B), and we provided a detailed functional analysis on the allosteric regulation of the Hb of the spectacled caiman (Fig.2C,D), and confirm the same mode of allosteric regulation in the Hbs of 13 other caiman, alligator and crocodile species. These results suggested that this unique property evolved in the common ancestor of extant crocodilians, and we recently confirmed it. Overall, the strong effect of blood CO2 and bicarbonate on Hb oxygenation during diving is to facilitate O2 delivery to sustain aerobic metabolism of tissues.
III. Physiology of hypoxia adaptation in the world’s highest-dwelling mammal.
Fig. 3. Colonization of high-altitude (HA) environments. (A) Hypothetical scenario in which fitness varies as a function of trait values in an ancestral, low-altitude (LA) environment. The trait value that confers highest fitness is denoted by a vertical dashed line. During colonization of the HA environment, hypoxia-induced plasticity in the trait leads to two possible scenarios. In Scenario 1 (B), the fitness function of the phenotype is shifted relative to that in the LA environment. The HA phenotypic optimum is denoted by the solid vertical line. Upon colonization of the HA environment, an adaptive plastic response moves the population mean phenotype part way to the new optimum, and selection on genetically based variation then shifts it the rest of the way. (B1) Hypothetical outcome of reciprocal-transplant experiment showing expression of the phenotype when highlanders and lowlanders are reared in native and nonnative environments. Arrow heads denote outcomes of reciprocal transplants (phenotypes expressed in the non-native environment). Highlanders and lowlanders exhibit a pronounced difference in phenotype when observed in their native habitats, and the reciprocal transplant reveals the loss of plasticity in highlanders. In Scenario 2 (C), the fitness function of the trait is the same in the LA and HA environments. Upon colonization of the HA environment, the hypoxia-induced plastic response shifts the mean trait value away from the global optimum. In HA natives, selection on genetically based trait variation counteracts the plastic change, thereby restoring the ancestral phenotype (i.e., the same phenotype expressed by lowland natives in the ancestral environment). (C1) Highlanders and lowlanders exhibit no difference in phenotype when observed in their native habitats, and the reciprocal transplant reveals the loss of plasticity in highlanders.
At the edge of the world, extreme low temperatures (-60ºC) and shortage of oxygen in the atmosphere (<10%) prevail all year around. What was previously thought to be an uninhabitable environment has now been challenged by the recent discovery of the highest-dwelling mammal: the leaf-eared mouse (Phyllotis vaccarum) at elevations >6700m. This new scientific record has changed our understanding and has challenged our current knowledge about altitudinal range limits and the physiological tolerances of small mammals. How is this small rodent able to cope with and thrive in conditions of extreme high elevations? is still yet to be answered. My current postdoctoral position is aimed at answering this question by experimentally examining mechanisms of hypoxia acclimation and adaptation in this species. Adaptation to hypoxia may include metabolic suppression in hypoxia tolerant ectotherms. However, these responses are not feasible as a permanent solution for highland endotherms. Therefore, the thermogenic physiological capacities of these species are challenged as they must sustain adequate metabolic heat production to fuel routine activities. In the scenario of colonization of a new high-altitude environment (i.e., when lowlander natives may move upwards looking for optimal temperature) (Fig.3), it is possible that the fitness optimum of hypoxia-compensating physiological traits at high-altitude may be shifted relative to the ancestral low-altitude environment.In principle, hypoxia-induced responses can either facilitate or impede genetic adaptation to the newly colonized high-altitude environment (Fig.3B,C). In both scenarios the mechanisms of hypoxia adaptation in highland natives are likely shaped by plastic responses. If these responses are costly, yet facilitate improved performance in the new high-altitude environment (i.e., is locally adaptive), selection may lead to genetic assimilation. The process results in the loss of plasticity (Fig.1,B1). Alternatively, if the environmentally induced response moves the mean phenotype further from the unchanged optimum, selection on genetically based trait variation can offset the maladaptive plasticity and restore the ancestral phenotype, a process known as genetic compensation (Fig. 1,C1). I am using a common-garden experimental design to examine physiological differences between natural populations of leaf-eared mice sampled from contrasting high- and low-altitude extremes of the species’ range. The experimental analysis of systemic physiology will involve measurements of whole-animal physiological performance (thermogenic capacity in hypoxia – V̇O2max) and a comprehensive set of subordinate traits in pedigreed, captive-bred highland and lowland mice. Results from these studies will provide insights into the relative contributions of genetic and environmentally induced changes in hypoxia-responsive phenotypes and the potential synergy or antagonism between them, advancing our understanding of physiological adaptation and the process by which complex physiological phenotypes evolve.
IV. Hypoxia acclimatization of highland and lowland mice and the potential for elevational range shifts in a warming world
How does acclimatization capacity affect a species’ ability to colonize novel environments?. This question has special conservation relevance in the context of upward elevational range shifts in a warming world. If acclimatization to hypoxia enables lowland natives to successfully colonize highland environments, highland natives may be “pushed off the top” due to competition. Alternatively, genetic adaptation of highland natives may confer a sufficiently durable home-field advantage that they can successfully outcompete lowland immigrants. Through a collaboration between Dr. Storz and Scott's Labs, I was able to address this question!. In this study, we report the results of an acclimation experiment to assess the performance capacities of highland and lowland deer mice (Peromyscus maniculatus) under increasing levels of hypoxia. Highland and lowland native populations were acclimated to oxygen concentrations that simulated a gradual ascent from sea level to an elevation of 6000m and we measured thermogenic aerobic capacities (VO2max) under acute exposure to cold at each 1000 m interval. Experimental results revealed evolved and plastic contributions to aerobic performance in hypoxia and yield insights into the factors that influence elevational range limits under a climate change scenario.
Figure 4. Experimental design to assess how the acclimatization capacity of lowlander deer mice affects the colonization of a new high-altitude environment. In red lowlander natives, in blue = highlander mice. Representatives of both populations were maintained in control or acclimated conditions. Acclimation consisted in stepwise weekly reductions in oxygen percentage that simulated an ascending expedition os 1000m/week.
Animal Models and Systems
Here are some of the animal models that I have had the opportunity to work with!
I generated this word cloud by adding the abstracts of my publications
