Efecto del manejo forestal en la herpetofauna de un bosque templado del occidente de Oaxaca, México / Effect of forest management on the herpetofauna of a temperate forest of western Oaxaca, Mexico

ResumenEl desarrollo de técnicas y tratamientos silvícolas tiene como objetivo principal el aumento de la productividad forestal, al mismo tiempo que minimiza el impacto sobre la diversidad. A pesar de ello, estas actividades modifican la estructura de la vegetación, así como el clima local, alterando la composición de las comunidades. El efecto de estos cambios puede ser mayor en aquellos grupos taxonómicos con alta sensibilidad a las alteraciones del hábitat, como es el caso de los anfibios y reptiles, que al ser los únicos vertebrados terrestres ectotermos, pueden verse seriamente afectados por las variaciones de clima local. El presente trabajo tiene como objetivo conocer las diferencias en diversidad de anfibios y reptiles en un bosque templado bajo dos tratamientos silvícolas (uno intensivo y otro de baja intensidad) y con diferentes tiempos de regeneración (uno, cinco y diez años) en la Sierra Sur del estado de Oaxaca, México. Se obtuvieron registros de 21 especies de herpetofauna (seis anfibios y 15 reptiles). La riqueza total de especies fue similar en ambos tratamientos; sin embargo, la composición varió entre sitios con diferentes tiempos de recuperación. La mayor abundancia de anfibios se presentó en los sitios con el tratamiento de baja intensidad, mientras que los reptiles fueron más abundantes en los sitios con el tratamiento intensivo. Se observó un mayor número de especies raras en los sitios intervenidos con el tratamiento intensivo, aunque los valores de diversidad verdadera de anfibios fueron similares entre tratamientos con intensidades diferentes, mientras que en los reptiles se observó una diversidad 33 % menor en los sitios bajo el tratamiento intensivo y un 28 % en los sitios con baja intensidad respecto al sitio control. Un Análisis de Complementariedad mostró una diferencia de hasta 86 % de disimilitud entre la composición de especies en sitios con el tratamiento intensivo. La intensidad del tratamiento estuvo asociada con un aumento en el número de especies, sin embargo la manera en que responden ante las modificaciones de hábitat depende en gran medida de las características poblacionales de cada especie, así como su habilidad de adaptación a las nuevas condiciones del hábitat.

Abstract:The development of silvicultural techniques has as main objective to maximize the production of timber, whereas at the same time minimize the impact generated during and after forest intervention in the local diversity. However, these activities change local climate, and this, in turn, alter the composition of natural communities. The effect of these changes may be greater in those taxonomic groups with high sensitivity to habitat disturbance, such as amphibians and reptiles, which are the unique terrestrial ectothermic vertebrates. The present study aims to know the differences in diversity of amphibians and reptiles in a temperate forest under two silvicultural treatments, one of low and the other of high intensity, as well as from one, five and ten years of regeneration since the last logging event, Sierra Sur of Oaxaca, Mexico. Records of 21 species of herpetofauna (six amphibians and 15 reptiles) were obtained. The total species richness was similar in both treatments; however, the composition varied between sites with different recovery times. Higher abundance of amphibian was presented on sites with the low-intensity treatment, while reptiles were more abundant at sites with intensive treatment. Compared to a mature forest without management, sites with intensive treatment have more rare species, although the values of true diversity of amphibians were similar between treatments with different intensities, while for reptiles sites under treatment showed less diversity that unmanaged site: 33 % for intensive treatment and 28 % at sites with low intensity with respect to one control site. Complementary Analysis showed a difference of 86 % between the compositions of species in sites with intensive treatment. The treatment intensity was associated with an increase in the number of species, but the way they respond to changes in habitat depends largely on the population characteristics of each species and its ability to adapt to new conditions. Rev. Biol. Trop. 64 (3): 931-943. Epub 2016 September 01.

Fisiologia de extremos: Digestão em répteis de alimentação esporádica / Extreme physiology: Digestion in intermittent-feeding reptiles / Fisiología de extremos: Digestión en reptiles de alimentación esporádica

Entre as diversas adaptações que os seres vivos apresentam em resposta às variáveis do ambiente, estão as mudanças adaptativas morfológicas e funcionais a curto e longo prazo que acontecem no sistema digestório em resposta ao padrão de alimentação. Em alguns répteis, tais adaptações vêm ao encontro da maximização dos recursos energéticos, os quais correlacionam os hábitos alimentares ao rendimento energético por meio do processo de regulação de órgãos específicos. Considerável número de artigos discute o desempenho do trato gastrointestinal e a influência de outros sistemas no auxílio a esse comportamento do sistema digestório em répteis, especialmente em pítons. Este trabalho teve por objetivo destacar e discutir as ações fisiológicas envolvidas no processo digestório e em outros sistemas em répteis que se alimentam esporadicamente. A atrofia e reconstrução alternadas do trato gastrointestinal em animais de hábitos alimentares infrequentes garantem a esses uma economia de energia em períodos de jejum e uma alta captação dos nutrientes no período digestivo. Essas alterações são acompanhadas por variações funcionais ácido-básicas, respiratórias e hemodinâmicas, e consequentemente por grandes mudanças na taxa metabólica, quando os estados de jejum e pós-prandial são comparados.

Short- and long-term morphological and functional adaptive changes in the digestive system related to the feeding habits are among the many adaptations living beings have in response to environmental variables. In some reptiles, such adaptations aim at maximizing the energy resources, which correlate the feeding habits with the energy performance through the regulation of specific organs. A considerable number of articles address the performance of the digestive tract and the influence of other systems in helping this digestive system behavior in reptiles, especially pythons. This paper has the purpose of highlighting and discussing the physiological actions involved in the digestive process and in other systems in reptiles that feed sporadically. The alternate atrophy and reconstruction of the gastrointestinal system in infrequent-feeding animals allow them to save energy during fasting and a high uptake of nutrients during digestion. These changes are accompanied by acid-base, respiratory and hemodynamic alterations, and therefore, by large changes in the metabolic rate, when comparing fasting and the post-prandial periods.

Entre las diversas adaptaciones que los seres vivos tienen, en respuesta a las variables ambientales, están los cambios adaptativos morfológicos y funcionales a corto y largo plazo que se producen en el sistema digestivo en respuesta al patrón de alimentación. En algunos reptiles, tales adaptaciones vienen a satisfacer la maximización de los recursos energéticos, que correlacionan los hábitos alimenticios con la eficiencia energética a través del proceso de regulación de órganos específicos. Números considerables de artículos analizan el rendimiento del tracto gastrointestinal y la influencia de otros sistemas para ayudar al sistema digestivo en los reptiles, especialmente las pitones. Este estudio tuvo como objetivo destacar y discutir las acciones fisiológicas que intervienen en el proceso digestivo y en otros sistemas en reptiles que se alimentan de forma esporádica. La atrofia y la reconstrucción alternadas del tracto gastrointestinal de animales de hábitos alimentarios infrecuentes, aseguran tales ahorros de energía durante los períodos de ayuno y una alta absorción de nutrientes en el período digestivo. Estos cambios van acompañados de variaciones funcionales ácido-básico, respiratorias y hemodinámicos y, consecuentemente por importantes cambios en la tasa metabólica, cuando se comparan los estados de ayuno y postprandial.

Autonomic control of cardiorespiratory interactions in fish, amphibians and reptiles

Control of the heart rate and cardiorespiratory interactions (CRI) is predominantly parasympathetic in all jawed vertebrates, with the sympathetic nervous system having some influence in tetrapods. Respiratory sinus arrhythmia (RSA) has been described as a solely mammalian phenomenon but respiration-related beat-to-beat control of the heart has been described in fish and reptiles. Though they are both important, the relative roles of feed-forward central control and peripheral reflexes in generating CRI vary between groups of fishes and probably between other vertebrates. CRI may relate to two locations for the vagal preganglionic neurons (VPN) and in particular cardiac VPN in the brainstem. This has been described in representatives from all vertebrate groups, though the proportion in each location is variable. Air-breathing fishes, amphibians and reptiles breathe discontinuously and the onset of a bout of breathing is characteristically accompanied by an immediate increase in heart rate plus, in the latter two groups, a left-right shunting of blood through the pulmonary circuit. Both the increase in heart rate and opening of a sphincter on the pulmonary artery are due to withdrawal of vagal tone. An increase in heart rate following a meal in snakes is related to withdrawal of vagal tone plus a non-adrenergic-non-cholinergic effect that may be due to humoral factors released by the gut. Histamine is one candidate for this role.

Control of respiration in fish, amphibians and reptiles

Fish and amphibians utilise a suction/force pump to ventilate gills or lungs, with the respiratory muscles innervated by cranial nerves, while reptiles have a thoracic, aspiratory pump innervated by spinal nerves. However, fish can recruit a hypobranchial pump for active jaw occlusion during hypoxia, using feeding muscles innervated by anterior spinal nerves. This same pump is used to ventilate the air-breathing organ in air-breathing fishes. Some reptiles retain a buccal force pump for use during hypoxia or exercise. All vertebrates have respiratory rhythm generators (RRG) located in the brainstem. In cyclostomes and possibly jawed fishes, this may comprise elements of the trigeminal nucleus, though in the latter group RRG neurons have been located in the reticular formation. In air-breathing fishes and amphibians, there may be separate RRG for gill and lung ventilation. There is some evidence for multiple RRG in reptiles. Both amphibians and reptiles show episodic breathing patterns that may be centrally generated, though they do respond to changes in oxygen supply. Fish and larval amphibians have chemoreceptors sensitive to oxygen partial pressure located on the gills. Hypoxia induces increased ventilation and a reflex bradycardia and may trigger aquatic surface respiration or air-breathing, though these latter activities also respond to behavioural cues. Adult amphibians and reptiles have peripheral chemoreceptors located on the carotid arteries and central chemoreceptors sensitive to blood carbon dioxide levels. Lung perfusion may be regulated by cardiac shunting and lung ventilation stimulates lung stretch receptors.

Excavatory cycle of Leposternon microcephalum Wagler, 1824 (Reptilia, Amphisbaenia) / Ciclo excavatorio de Leposternon microcephalum Wagler, 1824 (Reptilia, Amphisbaenia)

The excavatory movements of the spade-snouted amphisbaenid Leposternon microcephalum (Reptilia, Squamata) was studied with the aid of videofluorscopy (X-ray) techniques. This allows the observation of skull and column movements along tunneling, and a more detailed motion observation, being so a novel approach for amphisbaenian excavatory rescarches. A single specimen of Leposternon microcephalum was kept in a glass terrarium filled with semoline, and filmed with a scopy (X-ray) machine. Fixed anatomical marks on the head of the specimen were put in drawings from the framed recordings. Selected sequences of the recordings were fragmented in isolated frames for motion observation. The analysis of the recordings revealed a repetitive pattern of excavatory cycles, with retreating and downward bending of the head before its upstroke to compact the substrate tunnel roof. Follows a dropping of the head, which lays over the substrate giving support for the next retreating and downward head bending. This is an essential step that was neglected in earlier cycle descriptions. The initial downward head bending was not previously properly described for spade-snouted amphisbaenians. The excavatory movements of spade-snouted amphisbaenians are usually treated as a two-stepped cycle, but the evidence that this excavatory cycle has three steps is given here.

Los movimientos excavatorios de la Amphisbaenia (culebrilla ciega), con hocico en forma de pala, Leposternon microcephalum (Reptilia: Squamata) se estudiaron con la ayuda de técnicas de videofluoroscopía (rayos X). Esto permite la observación de los movimientos del cráneo y columna, a lo largo de túneles, y una propuesta más detallada, siendo un enfoque novedoso para investigaciones de la culebrilla ciega excavadora. Un solo espécimen de Leposternon microcephalum se mantuvo en un terrario de vidrio lleno de semolina, y fue filmado con una máquina de escopía (rayos X). Se fijaron marcas anatómicas en la cabeza de éste y luego fueron dibujadas desde las grabaciones. Las secuencias seleccionadas de las grabaciones fueron fragmentadas en fotogramas aislados de la observación del movimiento. Los análisis de las grabaciones revelaron un patrón repetitivo de ciclos excavatorios, con la retirada y doblamiento hacia abajo de la cabeza, antes de su movimiento hacia arriba para compactar el sustrato del techo del túnel. Sigue una caída de la cabeza, que se pone sobre el apoyo del sustrato para la próxima retirada y doblamiento hacia abajo de la cabeza. Esto es un paso esencial que es descuidado en las descripciones anteriores del ciclo. La primera flexión baja de la cabeza no fue debidamente descrita anteriormente para Amphisbaenia con hocico en forma de pala. Los movimientos excavatorios de estos animales suelen ser tratados como un período de dos ciclos intensificados, pero la evidencia que este ciclo excavatorio consta de tres pasos, se dan aquí.

Comparative study for some physiological parameters in the three species of the snakes from different regions of Egypt during the hibernation

The aim of this study was to compare some physiological parameters in three species of snakes [Psammophis schokari aegyptius [from Aswan], Psammophis schokari schokari [from Al-Wahat] and Psammophis sibilans sibilans [from Mansoura]] during the winter. Physiological parameters including thyroid hormones [T3 and T4], thyroid stimulating hormone [TSH], insulin hormone, calcium, iron, sodium, potassium and cholesterol, were recorded in the three species of the snakes. The results showed that serum TSH, T4, insulin hormones and iron were lower in the serum of Psammophis schokari aegyptius than the other two species. Conversely, all other parameters, i.e. T3, Na, K and calcium increased significantly in the serum of Psammophis schokari aegyptius than in the other species. On the other hand, a higher level of cholesterol was found in the serum of Psammophis schokari schokari than that in the other two species. Level of cholesterol in the serum of Psammophis sibilans sibilans was lower than the other two species

Evolution of circadian organization in vertebrates

Circadian organization means the way in which the entire circadian system above the cellular level is put together physically and the principles and rules that determine the interactions among its component parts which produce overt rhythms of physiology and behavior. Understanding this organization and its evolution is of practical importance as well as of basic interest. The first major problem that we face is the difficulty of making sense of the apparently great diversity that we observe in circadian organization of diverse vertebrates. Some of this diversity falls neatly into place along phylogenetic lines leading to firm generalizations: i) in all vertebrates there is a "circadian axis" consisting of the retinas, the pineal gland and the suprachiasmatic nucleus (SCN), ii) in many non-mammalian vertebrates of all classes (but not in any mammals) the pineal gland is both a photoreceptor and a circadian oscillator, and iii) in all non-mammalian vertebrates (but not in any mammals) there are extraretinal (and extrapineal) circadian photoreceptors. An interesting explanation of some of these facts, especially the differences between mammals and other vertebrates, can be constructed on the assumption that early in their evolution mammals passed through a "nocturnal bottleneck". On the other hand, a good deal of the diversity among the circadian systems of vertebrates does not fall neatly into place along phylogenetic lines. In the present review we will consider how we might better understand such "phylogenetically incoherent" diversity and what sorts of new information may help to further our understanding of the evolution of circadian organization in vertebrates.

The role of CO2/pH chemoreceptors in ventilatory control

It now appears that at least some members of all classes of vertebrates exhibit ventilatory responses to changes in CO2/pH per se, including fishes. With the transition from aquatic to aerial respiration, there is an increase in the sensitivity of animals to this complex of stimuli, an increase in the variety of putative receptors possibly involved in eliciting ventilatory responses and an increase in the relative importance of this complex of stimuli in the genesis of resting ventilation. The variety of CO2-sensitive chemoreceptors present in air-breathing lower vertebrates adds considerable complexity to experimental studies of ventilatory responses to CO2/pH. Because of the locations, discharge characteristics and reflex effects of the different receptor groups, most air-breathing lower vertebrates show different responses to increases in CO2/[H+] due to cerebral ischemia, anoxia, metabolic acidosis and environmental hypercarbia. In some cases the differences are only quantitative, while in other cases the responses are qualitatively very different. These differences appear to reflect differences in the relative strength of the reflexes elicited by the various receptor groups and the net sum of their modulating influences when CO2/pH are altered via different routes. Although the situation is simpler in the higher vertebrates, in all cases the input from all of the CO2/[H]-sensitive receptors appears to act as a biasing input which summates with other afferent information to modulate respiratory motor output, even in those species that breathe intermittently.

Regulation of acid-base status in ectothermic vertebrates: the consequences for oxygen pressures in lung gas and arterial blood

Extensive literature reports a negative deltapHa/deltat in ectothermic vertebrates, but data are scarce as to its consequences for O2 transport. In reptiles, the negative delta-pHa/delta-t results from an elevated lung gas PCO2 (PACO2) at higher temperatures, implying a corresponding fall of PAO2. In parallel, arterial PO2 rises with temperature, due to a combination of central vascular shunt and decreasing Hb O2 affinity. As a result, the PO2 gradient between lung gas and blood (PA-aO2) becomes reduced at higher temperatures. In amphibians, the negative delta-pHa/delta-t results from combined cutaneous and pulmonary CO2 elimination. We propose that this leads to a rather temperature-independent lung gas PO2. Moreover, our calculations suggest that resting reptiles and amphibians maintain a relatively large PA-aO2 also at high temperatures. The negative delta-pHa/delta-t in teleost fish is generally considered to be a result of modulated plasma [HCO3-]. Recent data from our laboratory suggest that acute pH adjustments at high temperatures may involve alterations of PaCO2 through gill ventilation, leading to a decrease of PaO2 with rising temperature.

Estivation in South American amphibians and reptiles

A number of amphibians and reptiles have cyclic behavior, becoming inactive with the coming of the dry season. In South America this pattern of activity is common, particularly in savannah-like vegetation. During the dry season amphibians burrow into the mud or soil, and either form a cocoon or increase the osmotic concentration of body fluids to reduce evaporative water loss. Some phyllomedusid tree frogs coat their body surface with skin secretion and excrete uric acid to minimize water loss. Reptiles also retreat into shelter deep enough to avoid temperature fluctuation during estivation or reduce metabolic response to temperature. Reduction of temperature sensitivity of the metabolism seems to be a strategy common to estivating amphibians and reptiles. Despite seasonal change of the environment, some species of reptiles are active all year round.

El órgano auditivo de la lagartija Sceloporus torcuatus: estudio anatómico y funcional / The hearing organ of lizard Sceloporus torcuatus: an anatomical and physiological study

Se hace una breve descripción de la anatomía del oído externo y de la fisiología auditiva de Sceloporus torcuatus. Se señala que la depresión formada por el conducto auditivo externo esta parcialmente cubierta por escamas de mayor tamaño que las normales, las que además tienen forma diferente al resto de las escamas de la región, por lo que se les dio un nombre especial, denominándolas escamas frontales del oído externo. Se describe detalladamente el conducto coclear, poniendo énfasis en la histología del mismo. También se describen algunos epitelios, tales como los de la papila basilar (órgano de la audición), las manchas de la lagena y la pared vestibular del conducto coclear, esta última se ha considerado en otros reptiles como tejido secreto. La similitud morfológica entre la pared vestibular del conducto coclear de esta especie, la estría vascular de los mamíferos y el tegumento vasculoso de las aves, sugiere semejanzas funcionales de estas estructuras. Se usaron potenciales evocados auditivos del tallo cerebral para estudiar esta especie reptiliana. Se encontró (con clics) el umbral de potenciales de estímulos auditivos a 40 dB

Evolutionary origins of the reptilian brain: the question of putative homologues of dorsal ventricular ridge. An overview and proposal

The reptilian brain is characterized by a structure that bulges into the lateral ventricle, called dorsal ventricular ridge (DVR). The DVR was originally considered to be a part of the basal ganglia, although more recent studies indicate that it may correspond to the dorsal part of the hemisphere. The anterior portion of the DVR has several connectional and functional similarities with parts of the mammalian neocortex, for which reason it has been claimed that the two structures can be considered as homologues. In this article I review the evidence supporting and refuting homology of the DVR with different telencephalic structures of mammals, concluding that it is still early to unequivocally ascribe structural correspondences between the different components in the two vertebrate classes. However, a way out of the problem is suggested by comparing the embryonic position of DVR with that of lateral cortex in the reptilian hemisphere. The lateral cortex is considered to be quite comparable in reptiles and mammals, and hence may be a good marker for the original position of the DVR. If the DVR originates dorsal to lateral cortex, it may be considered comparable to parts of the mammalian neocortex, while if it develops in its same position or ventral to it, it may not correspond to the neocortex. Early embryological work indicated that the DVR develops in the same position as the lateral cortex, but arises as a late migration wave, after cells destined to lateral cortex are generated. In other words, instead of being interposed between dorsal and lateral cortices, the DVR may originate in a position overlapping with lateral cortex. If this alternative turns out to be the case, it may imply that the DVR arose de novo, through an extension of the ancestral period of neuroblast proliferation. As a consequence, there may be no structures comparable to it in other vertebrate classes. Finally, it is also proposed that, regardless of whether the DVR and the extrastriate neocortex can or cannot be considered phylogenetic homologues, some of the integrative functions performed by them might have a common evolutionary origin, that became localized in the reptilian DVR and in the mammalian extrastriate neocortex