A Mountain or a Plateau? Hematological Traits Vary Nonlinearly with Altitude in a Highland Lizard

CONACYT 178723High-altitude organisms exhibit hematological adaptations to augment blood transport of oxygen. One common mechanism is through increased values of blood traits such as erythrocyte count, hematocrit, and hemoglobin concentration. However, a positive relationship between altitude and blood traits is not observed in all high-altitude systems. To understand how organisms adapt to high altitudes, it is important to document physiological patterns related to hypoxia gradients from a greater variety of species. Here, we present an extensive hematological description for three populations of Sceloporus grammicus living at 2,500, 3,400, and 4,300 m. We did not find a linear increase with altitude for any of the blood traits we measured. Instead, we found nonlinear relationships between altitude and the blood traits erythrocyte number, erythrocyte size, hematocrit, and hemoglobin concentration. Erythrocyte number and hematocrit leveled off as altitude increased, whereas hemoglobin concentration and erythrocyte size were highest at intermediate altitude. Additionally, lizards from our three study populations are similar in blood pH, serum electrolytes, glucose, and lactate. Given that the highest-altitude population did not show the highest levels of the variables we measured, we suggest these lizards may be using different adaptations to cope with hypoxia than lizards at low or intermediate altitudes. We discuss future directions that research could take to investigate such potential adaptations

Histological Characteristics of Gills and Dorsal Skin in Ambystoma leorae and Ambystoma rivulare: Morphological Changes for Living at High Altitude

Vertebrates exhibit structural changes in their cardiovascular and gas exchange systems in response to hypoxic conditions in high altitude environments. In highland neotenic mole salamanders, as other amphibians, the majority of gases exchange is carried out for skin and gills. But, in high altitude environments, the available oxygen is lower than it is in the air thus, the scarcity of oxygen limits the survival of organisms. Many studies on this subject have focused on understanding the hematological mechanisms that amphibians exhibit in response to hypoxia. However, little is known about possible morphological changes in respiratory structures that may permit increased gas exchange during respiration in high altitude amphibians like Ambystoma leorae and A. rivulare, two threatened Mexican salamander species. The aim of the present study was to describe and compare the histological characteristics of the gills and dorsal skin of A. leorae and A. rivulare from populations at low and high altitudes. We found that, in comparison to lowland organisms, highland ones exhibited more pronounced skin folds, greater numbers of secondary branches in the gills, thinner dorsal and gill epidermises, and greater quantity of melanin surrounding the gill blood vessels. These differences permit a greater capacity for gas exchange and also increase thermoregulatory capacity in high altitude environments.Consejo Nacional de Ciencia y Tecnología (grant 178723) Secretaría de Medio Ambiente y Recursos Naturales (SGPA/DGVS/02407/13)

Variation in Reproductive Behavior and Sexual Signals Within and Among Populations of an Incipiently Speciating Lizard

Discrete variation in colorful sexual signals is often associated with variation in reproductive tactics or strategies. Many taxa with intrapopulation color polymorphisms also exhibit variation among populations or among closely related species in the frequency of color morphs, the number of morphs present within a population, or which particular colors are used as signals. These patterns may be important for understanding speciation because theoretical and empirical studies indicate that both color polymorphism and alternative reproductive tactics may be associated with elevated diversification rates. I studied variation in throat color, an important sexual signal, within and among populations of the mesquite lizard (Sceloporus grammicus) species complex. The S. grammicus species complex is considered a possible example of incipient speciation due to high levels of variation in chromosome number, habitat use, reproductive cycles, and life history. My first chapter confirms this variability in female life history, and the rest of my dissertation is the first research to address sexual signals in S. grammicus. I performed a broad geographic survey of throat color polymorphisms and used laboratory behavioral trials and molecular phylogenetics to investigate the meaning and evolutionary context of the polymorphisms I observed. I found that male S. grammicus within a single population exhibited either orange, yellow, and blue throat color morphs or orange, yellow, and white throat color morphs. In no case did I observe the blue male morph and the white male morph in the same population. I found that both the orange/yellow/blue and orange/yellow/white polymorphisms in males were associated with variation in male aggression level, but the meanings of particular colors were different between the two populations I studied. I also found that females performed more rejection behaviors towards allopatric males when those males were of a color morph that did not occur in the female's home population than when the allopatric male was of a color morph that did occur in the female's home population. Finally, I constructed a phylogeny of the populations I had sampled and used ancestral state reconstruction to establish that the white male morph in the S. grammicus complex has originated at least twice

Data from: Is it the song or the singers? Acoustic and social experiences shape adult reproductive tactics and condition

When sexual signals are perceived during growth and development they can provide information regarding the social conditions likely to be encountered as an adult. Perception of cues related to the presence and density of future mates and potential competitors can result in altered adult phenotypes. Previous studies have shown that adult male Teleogryllus oceanicus field crickets from a Kauai, Hawaii population reared alone and without hearing conspecific song are more phonotactic than those reared with song. These naïve males also reduce investment in body size and immunity. Here we examined whether another source of population density information, the presence of other males, affects behavior, size, and immunity. Specifically, we examined satellite behavior as evidenced by strength of phonotaxis, body condition, and immune response in males reared singly and in groups in the presence and absence of conspecific song. Body condition did not vary with rearing density, and immune response did not vary with either acoustic environment or rearing density. Interestingly, group-housed males were more phonotactic than singly-housed males. This pattern was largely driven by the low levels of phonotaxis exhibited by males that were singly-housed in the presence of conspecific song. These findings suggest that males respond to social cues in addition to conspecific song, but that these cues do not necessarily provide concordant information

Balenger_cricket_density_data

Balenger_cricket_density_dat

Female Preference for Sympatric vs. Allopatric Male Throat Color Morphs in the Mesquite Lizard (Sceloporus grammicus) Species Complex

Color polymorphic sexual signals are often associated with alternative reproductive behaviors within populations, and the number, frequency, or type of morphs present often vary among populations. When these differences lead to assortative mating by population, the study of such polymorphic taxa may shed light on speciation mechanisms. We studied two populations of a lizard with polymorphic throat color, an important sexual signal. Males in one population exhibit orange, yellow, or blue throats; whereas males in the other exhibit orange, yellow, or white throats. We assessed female behavior when choosing between allopatric and sympatric males. We asked whether females discriminated more when the allopatric male was of an unfamiliar morph than when the allopatric male was similar in coloration to the sympatric male. We found that female rejection of allopatric males relative to sympatric males was more pronounced when males in a pair were more different in throat color. Our findings may help illuminate how behavioral responses to color morph differences between populations with polymorphic sexual signals contribute to reproductive isolation

A Mountain or a Plateau? Hematological Traits Vary Nonlinearly with Altitude in a Highland Lizard.

CONACYT 178723High-altitude organisms exhibit hematological adaptations to augment blood transport of oxygen. One common mechanism is through increased values of blood traits such as erythrocyte count, hematocrit, and hemoglobin concentration. However, a positive relationship between altitude and blood traits is not observed in all high-altitude systems. To understand how organisms adapt to high altitudes, it is important to document physiological patterns related to hypoxia gradients from a greater variety of species. Here, we present an extensive hematological description for three populations of Sceloporus grammicus living at 2,500, 3,400, and 4,300 m. We did not find a linear increase with altitude for any of the blood traits we measured. Instead, we found nonlinear relationships between altitude and the blood traits erythrocyte number, erythrocyte size, hematocrit, and hemoglobin concentration. Erythrocyte number and hematocrit leveled off as altitude increased, whereas hemoglobin concentration and erythrocyte size were highest at intermediate altitude. Additionally, lizards from our three study populations are similar in blood pH, serum electrolytes, glucose, and lactate. Given that the highest-altitude population did not show the highest levels of the variables we measured, we suggest these lizards may be using different adaptations to cope with hypoxia than lizards at low or intermediate altitudes. We discuss future directions that research could take to investigate such potential adaptations

Histological Characteristics of Gills and Dorsal Skin in Ambystoma leorae and Ambystoma rivulare: Morphological Changes for Living at High Altitude

Vertebrates exhibit structural changes in their cardiovascular and gas exchange systems in response to hypoxic conditions in high altitude environments. In highland neotenic mole salamanders, as other amphibians, the majority of gases exchange is carried out for skin and gills. But, in high altitude environments, the available oxygen is lower than it is in the air thus, the scarcity of oxygen limits the survival of organisms. Many studies on this subject have focused on understanding the hematological mechanisms that amphibians exhibit in response to hypoxia. However, little is known about possible morphological changes in respiratory structures that may permit increased gas exchange during respiration in high altitude amphibians like Ambystoma leorae and A. rivulare, two threatened Mexican salamander species. The aim of the present study was to describe and compare the histological characteristics of the gills and dorsal skin of A. leorae and A. rivulare from populations at low and high altitudes. We found that, in comparison to lowland organisms, highland ones exhibited more pronounced skin folds, greater numbers of secondary branches in the gills, thinner dorsal and gill epidermises, and greater quantity of melanin surrounding the gill blood vessels. These differences permit a greater capacity for gas exchange and also increase thermoregulatory capacity in high altitude environments.Consejo Nacional de Ciencia y Tecnología (grant 178723) Secretaría de Medio Ambiente y Recursos Naturales (SGPA/DGVS/02407/13)