Maria Edenilce P. Batista, Antônio Álamo F. Saraiva, Flaviana J. De Lima
et al.
We describe a new genus of Leliacladus Batista & L.Kunzmann with the type species Leliacladus (Brachyphyllum) castilhoi (Duarte, 1985) Batista & L.Kunzmann gen. nov. et comb. nov., a rare fossil conifer that has been described from the Aptian (Lower Cretaceous) Romualdo Formation of the Araripe Basin, northeastern Brazil. We decided to leave this new fossil-genus unasigned to any existing family as it does not display sufficient number of anatomical characters. We re-studied the type material of the type species as well as we described additional new material from the Aptian Crato Formation of the same basin. The more recently found fossil materials include large portions of leafy shoots excavated from laminated lacustrine limestones. In contrast to the type material, the new material shows the replacement of organic matter by iron oxide, which is suitable for investigating anatomical features of the wood and leaves. The material allowed for a reappraisal of the systematic position of the fossil plant. Together, the morphological and anatomical characters revealed sufficient evidence to separate the conifer from Brachyphyllum and accommodate it in a new fossil-genus. Leliacladus gen. nov. is defined by the presence of comparatively thick and short claviform lateral branches, and the absence of thinner ultimate order branches with gradual tapering axes. The wood is characterized by dense tracheids with uniseriate pitting in the radial walls and cross-fields that possess one or two large pits. The rays are one to three cells high. The epidermises of the densely and helically arranged scale leaves show non-papillate cyclocytic stomatal complexes slightly sunken that are mostly scattered and randomly arranged across the abaxial surface. This combination of characters suggests the material belongs to the conifer families Podocarpaceae or Cheirolepidiaceae. The arrangement of the sparsely branched, but woody shoots of Leliacladus castilhoi gen. nov. et comb. nov. suggest a hypothetical candelabra-like growth habit of the plant, and the remarkable thickness of the axes suggests a hypothetical xeromorphic adaptation to the semiarid paleoenvironment.
According to the Trivers–Willard hypothesis (TWH), when the mother's condition around conception influences the future reproductive success of male and female offspring differently, the adjustment of offspring sex ratio (SR) to maternal condition will increase the parents’ fitness. The TWH has been tested in several taxa, including humans where socioeconomic status as an index of condition has been widely used. The results are inconsistent, possibly because the preconditions of the TWH are not always met. To investigate the preconditions and prediction of the TWH in the contemporary Hungarian population, we collected data by an online questionnaire on self-perceived childhood living standard, the number of children and the sex of the respondents’ siblings. We found no sex-specific relationship between reproductive success and childhood living standards, thus the precondition of the TWH was not met. We found no relationship between socioeconomic status and offspring SR when data from the whole country was used, but there was a tendency in the predicted direction when we used data from Budapest and considered the SR of only those family members who were born under similar conditions. Similar approaches should be preferred in the future to avoid noise caused by changing status during the reproductive lifespan.
Aisylu G. Ibragimova, Artyom V. Gusarov, Larisa A. Frolova
Remains of <i>Rhynchotalona latens</i> (Sarmaja-Korjonen, Hakojärvi et Korhola 2000) were found in the bottom sediments of several glaciogenic lakes in northwestern Russia. Subfossil remains of the species were noted both in the bottom sediments of the Late Pleistocene and Mid-Holocene. We discovered a rare species, <i>R. latens</i>, in the bottom sediments of Lake Medvedevskoye (Karelian Isthmus). This species prefers shallow oligo-mesotrophic lakes with organic sediments and has attracted the interest of scientists around the world as it is considered a glacial relict and has recently been found in surface sediments and as a living population in Finland and Russia.
Joseph R. McAuliffe, Leslie D. McFadden, Lyman P. Persico
et al.
In what are now the warm deserts of the American Southwest, direct effects of changing climate on plant distributions are typically viewed as the principal driver of vegetation changes that followed the late Pleistocene–Holocene transition (LPH). However, at a semi-arid site in the eastern Mojave Desert, the transition to modern, shrub-dominated desert scrub on xeric, south-aspect hillslopes occurred only after the erosion of relatively thick soils toward the end of the mid-Holocene. Soils with well-developed Bt horizons began to form in the late Pleistocene on both north- and south-aspect hillslopes through the entrapment and accumulation of aeolian sediments in coarse colluvium. Those soils are capable of absorbing and retaining substantial moisture and support relatively dense stands of perennial C<sub>4</sub> grasses that have diffuse, fibrous root systems. The age of alluvial deposits on the basin floor indicates a surge in sediment production through the erosion of some of those hillslope soils toward the end of the mid-Holocene. However, that erosion was largely limited to the more xeric, more sparsely vegetated, south-aspect hillslopes. The soils formed on mesic north-aspect hillslopes remain largely non-eroded to the present day, demonstrating the central role of vegetation in modulating erosion and sediment supply. The loss of soils from south-aspect hillslopes fundamentally changed the capacity of those environments to absorb and store moisture, and altered the depth and temporal durations of plant-available moisture. Those hydrological changes drove a loss of perennial C<sub>4</sub> grasses and a transition to dominance by xerophytic plants—shrubs with deeper taproots capable of extracting moisture stored within bedrock joints and fractures, and shallow-rooted succulent plants that store moisture internally. Following the LPH, vegetation change at the site apparently occurred in two distinct phases separated in time: (1) initial vegetation changes driven directly by increasing climatic aridity and (2) subsequent changes linked to the later episode of soil erosion. Although climate shifts ultimately generate vegetation changes, the proximate mechanisms to which plants directly respond can lag far behind climatic transitions and involve complex relationships of vegetation, soils, and changing soil hydrologic conditions.
The evolutionary history of gars, an ancient group of ray-finned fishes, is excellently documented in the fossil record.
These fishes are notable for how little the anatomy of extant species differs from that of their earliest known relatives
from over 150 million years ago. As such, the low species richness of the gar crown group is thought to reflect the diversity of this clade over most of their history. Here, I describe the skeleton of a new gar species from the Eocene Willwood
Formation of Wyoming, USA. Numerous features, including a shortened skull, ornamented external cranial bones, and
microteeth ally the new species with Cuneatini, an obscure clade of gars restricted to the Eocene of southwestern North
America. Yet, Cuneatus maximus sp. nov. is more than twice as large as its closest relatives. The holotype of the new
species preserves a partial palate, providing new information about the anatomy of this poorly known cranial region
in cuneatins. Phylogenetic analysis of gars with the new species C. maximus included implies a diversification of cuneatins in North America following the Cretaceous/Paleogene extinction. The presence of large-bodied stem-gars in the
Eocene Willwood Formation also suggests that the fish fauna of this region was reminiscent of present-day ones from
the American southeast. The discovery of C. maximus emphasizes the propensity of the fossil record to significantly
increase the diversity and biogeographic range of even the most depauperate lineages.
Christian Klug, Laure Bonnaud-Ponticelli, Jaruwat Nabhitabhata
et al.
Abstract Sigurd von Boletzky was a cephalopod researcher who was world-renowned for his enthusiasm for his field of research, for his friendly and calm personality, and, of course, his publications. He dedicated most of his life as active researcher on the development, biology and evolution of coleoids. Nevertheless, he was always curious to learn about other cephalopods as well. Sigurd passed away in Switzerland on September 28th 2020. We dedicate this text and volume to his memory.
The “condylarth” genus Hyopsodus is diverse and abundantly represented in Eocene mammalian faunas of North America.
In contrast, fossil specimens of Hyopsodus are rather sparse in Eurasia. Only four species of Hyopsodus are known from
Asia and two from Europe, as compared to the 18 species of Hyopsodus described from North America. Here, we report a
new species of Hyopsodus, Hyopsodus arshantensis sp. nov., from the middle part of the Arshanto Formation in the Erlian
Basin, Inner Mongolia, China. The holotype and only specimen of the new species, a right mandible with m1–m2, exhibits
a unique combination of characters on m1–m2 not present in other species of Hyopsodus, including a moderately lophodont
crown, a long trigonid without a paraconid, an obliquely aligned protolophid, an angle between the cristid obliqua and
the posthypocristid slightly greater than 90°, a midline position of the hypoconulid, and a relatively large entoconid. The
m1–m2 morphology of H. arshantensis is intermediate between specimens of Hyopsodus from the Wasatchian and Uintan
North American Land Mammal Ages (NALMA), and is comparable to that of Hyopsodus from the Bridgerian NALMA.
Moreover, its relatively large size is near the size range present among the late Bridgerian species of Hyopsodus. Based
on those similarities, in combination with a few fossil mammals from overlying layers, the middle part of the Arshanto
Formation could be correlated in part to the late Bridgerian, and the upper part of the Arshanto Formation may bracket the
time interval equivalent to the Bridgerian/Uintan boundary. That proposed correlation and somewhat different faunas recognized
within the Arshanto Formation suggest that it may be necessary to subdivide the Arshantan Asian Land Mammal
Age (ALMA) and/or redefine the Arshantan/Irdinmanhan ALMA boundary in future comprehensive studies.
A unique lead seal-matrix with majuscule legend: LUCIANI PRESBITERI belonging to a priest was found by the Romanesque castle church in Giebło. The name of its owner is mentioned in written sources from the years 1325–1327 as plebanus ecclesie de Kebel. As PRESBITER he probably didn’t enjoy all privileges that the collator usually bestows on a parish priest on his property. Possibly for that reason he had his matrix made in an easy-to-process material, infrequently used for such objects in this part of Europe. The use of this raw material suggests someone who tried avoid the high costs of making the item. Special attention is merited by the composition of a fleur-de-lis crowned with the cross engraved on the seal face that resembles a heraldic device. The repetition of a schematic lily flower on the reverse of the matrix shows the special importance of this sign (identified in medieval time with the Blessed Virgin Mary); this symbol was treated in this way by, for example, Cistercians. By presenting his name in the company of these symbols, Lucianus gave his seal strength and credibility.
Resumen. Este trabajo reseña la historia del desarrollo de la palinología del Cuaternario en la Argentina durante los últimos 90 años. Se focaliza en el desempeño y las publicaciones de los investigadores en dicha disciplina en el contexto del desarrollo de las políticas institucionales y su relación con los procesos económicos y políticos, más que en el aporte que estas contribuciones han hecho a la comprensión de la historia de la vegetación, el clima y los ecosistemas. Se han priorizado los momentos y las contribuciones más significativos que representan hitos de esta historia. La reseña se ha dividido en cuatro períodos: (1) los comienzos (1929–1966); (2) la continuación (1977–1989); (3) el desarrollo (1990–2001) y (4) la consolidación (2002 al presente). En los últimos 20 años ha habido un gran impulso del análisis polínico del Cuaternario en la Argentina y, por lo tanto, se consideran finalmente los progresos y desafíos futuros en esta disciplina.
Palabras clave. Análisis palinológico. Holoceno. Pleistoceno.
Abstract. QUATERNARY PALYNOLOGY HISTORY IN ARGENTINA: LOOKING BACK AT NINETY YEARS SINCE ITS BEGINNING. This paper reviews the history of the development of the Quaternary palynology in Argentina during the last ninety years. This work focuses on the performance and publications by researchers in this discipline in the political and economic context of the development of institutional policies, rather than on advances about the history of vegetation, climate and ecosystems. The most significant moments and contributions that represent specific milestones of this history have been prioritized. This revision has been divided into four periods: (1) the beginnings (1929–1966); (2) the following years (1977–1989); (3) the development (1990–2001); and (4) the consolidation (2002 to present). In the last twenty years there has been an enormous development in Quaternary pollen analysis in Argentina, and thus future developments and challenges in this area are finally considered.
Key words. Palynological analysis. Holocene. Pleistocene.
Resumen. Los escamosos conforman un exitoso grupo de reptiles que incluye más de 9.600 especies actuales. Su evolución en América del Sur, escasamente ilustrada por un registro fósil incompleto y episódico, es consecuencia de la compleja historia geológica y paleoclimática de esta parte del mundo. El registro del Mesozoico está concentrado principalmente en Argentina y Brasil, con menor presencia en Bolivia. Los principales clados de reptiles escamosos (Iguania y Scleroglossa) aparecen en el registro durante el Cretácico, donde las serpientes eran comunes y diversas, con algunas de las más primitivas formas terrestres. Los escamosos del Paleógeno y Neógeno provienen principalmente de Argentina, Bolivia, Brasil, Colombia, Perú y Venezuela. Los lagartos eran poco comunes en el Paleógeno pero las serpientes muestran una importante diversidad que incluye al menos dos boideos actuales (Boa y Corallus) y formas extintas. El Mioceno es especialmente relevante ya que se reconocen por primera vez algunos géneros actuales de Iguanidae (Liolaemus, Pristidactylus), Teiidae (Tupinambis) y otros Boidae (Eunectes, probablemente Epicrates), aunque también existen géneros extintos. La primera ocurrencia de Colubridae corresponde al Mioceno temprano, mientras que los Scolecophidia aparecen en el registro durante el Mioceno medio y los Viperidae en el Mioceno tardío. El más antiguo Amphisbaenia sudamericano es registrado en el Plioceno y los primeros Gekkonidae, Anguidae y Elapidae son del Pleistoceno. La mayoría de los escamosos del Pleistoceno y Holoceno corresponden a géneros actuales, incluyendo algunas especies vivientes.
PALABRAS CLAVE. Lagartos. Anfisbenios. Serpientes. Mesozoico. Cenozoico. América del Sur.
Abstract. ADVANCES IN THE KNOWLEDGE OF THE CONTINENTAL FOSSIL SQUAMATE REPTILES OF SOUTH AMERICA. The squamates are a successful group of reptiles which includes more than 9,600 extant species. Their evolution in South America, scarcely illustrated by the incomplete and episodic fossil record, is a consequence of the complex geological and paleoclimatic history of this part of the world. The Mesozoic squamate record is concentrated in Argentina and Brazil, with less presence in Bolivia. Both major squamate clades (Iguania and Scleroglossa) are present during the Cretaceous, where snakes were common and diverse, involving some of the most primitive terrestrial forms. Paleogene and Neogene squamates were mainly recorded in Argentina, Bolivia, Brazil, Colombia, Peru, and Venezuela. Lizards were uncommon in Paleogene deposits but snakes showed an important diversity which included at least two extant boid snakes (Boa and Corallus) and extinct forms. The Miocene is especially relevant because of the first recognition of some extant genera of Iguanidae (Liolaemus, Pristidactylus), Teiidae (Tupinambis), and other Boidae (Eunectes, probably Epicrates), although extinct genera were also present. First occurrence of Colubridae is from the early Miocene, whereas Scolecophidia appears in the middle Miocene, and Viperidae in the late Miocene. The earliest Amphisbaenia of South America is recorded in the Pliocene, and the earliest Gekkonidae, Anguidae and Elapidae come from the Pleistocene. Most Pleistocene and Holocene squamate remains correspond to living genera, including some extant species.
KEY WORDS. Lizards. Amphisbaenians. Snakes. Mesozoic. Cenozoic. South America.
Mariano Bond, Guillermo López, Marcelo A. Reguero
et al.
The Fray Bentos Formation, with outcrops in the Uruguayan and the Argentinean provinces of Corrientes and Entre Ríos, has yielded several fossil vertebrates, mainly mammals, that permit its reference to the Deseadan land-mammal age (upper Oligocene?). At the Argentine sites, dasypodidid edentates (Euphractinae) and caviomorph rodents (Chinchillidae and Cephalomyidae) not previously cited for these localities, were recorded together with notoungulates Leontinidae, Mesotheriidae (Trachyteriinae), Interatheriidae (Interatheriinae), Hegetotheriidae (Hegetotheriinae) and Archaeohyracidae. The most abundant remains belong (as in most South American Tertiary associations), to representatives of the Order Notoungulata, which allow its assignment to the Deseadan land-mammal age s. l.: Prohegetotherium (Hegetotheriidae, Hegetotheriinae) and Trachyterus (= "Ameghinotherium"; Mesotheriidae, Trachyterinae) are characteristic of this age. The presence of an Archaeohyracidae, the biocron of which extends to the Deseadan land-mammal age, also agrees with this temporal assignment of the bearing sediments. The remains referred to Leontinidae belong to a different taxon from that described for the Fray Bentos Formation in Uruguay. This family has been recorded from the Mustersan to the Colhuehuapian land-mammal ages, but is characteristic of the Deseadan land-mammal age. Chinchillidae and Cephalomyidae are recorded since the Deseadan land-mammal age. However, certain features of the specimens from Corrientes Province are more similar to Colhuehuapian forms than to the Deseadan one. Dasypodidae is represented by a new taxon of Euphractinae Euphractini and fragmentary remains of a morphotype similar to Machylotherium. This genus is recorded in the Casamayoran and Mustersan land-mammal ages of Patagonia (Eocene). Consequently, this taxon does not conform with the age proposed for this formation.
KEY WORDS. Argentina. Corrientes. Fray Bentos Formation. Deseadan land-rnammal age. Mammals.
Rosendo Pascual, María L. Balarino, Daniel E. Udrizar Sauthier
The history of South American mammals has been episodic, apparently "stratified", and the "strata" relatively few in number and, as a rule, sharply and clearly separable. This is a consequence of the physical history of the continent. The fossil record shows that there were two great episodes characterized by drastic turnovers of mammal communities; both appear related to two of the most drastic physical changes withstood by the continent. The oldest episode is related to the separation of Africa from the other Gondwanan continents (shaping the primordial outlines of the eastern coast of the incipient Southern Atlantic Ocean), and to a sporadic connection of the South American plate with the North American plate. This led to the first great turnover: with the exception of two Gondwanan taxa (Monotremes and Gondwanatheres), and probably another one (Dryolestida), all the Gondwanan mammals (all non-tribosphenic taxa) became extinct, and were "replaced" by Laurasian tribosphenic marsupial and placental immigrants. Because of the early extinction (early Paleocene) of the Gondwanan non-tribosphenic survivors, and the subsequent isolation of the continent (including, at least, the Antarctic Peninsula) unique communities solely composed of quite endemic (native) marsupials and placentals were built up. As a consequence of the inter-American connection via the newborn Central America, an increasing biotic interchange began. The second great turnover, involving dispersal, extinction and survival, built up quite peculiar mammalian communities. These are the new basic mammal communities that, after the "Megafaunal Extinction" and the addition of a few and selected immigrants, distinguish the present Neotropical Region. Apparently this second great turnover was accomplished by replacement, not by displacement, as long thought. The failure to find mammals in rocks representing the K-T transition, has no record to analyze the modus operandi of the transcendental first turnover.
KEY WORDS. South American land-mammals. K-T. Tertiary-Pleistocene. Dispersal. Turnover. Extinction. Survival.
Gabriel Bollini, Juan P. Atencio, Sonia E. Colantonio
RESUMEN En el presente trabajo se comparan los diámetros odontométricos mesio-distal y vestíbulo-lingual en 63 cráneos de individuos masculinos, con dentición adulta, correspondientes a cuatro series craneanas argentinas: Arroyo Seco 2, Río Negro, Pampa Grande y Delta del Paraná. Se analizaron la mayoría de las piezas dentales, solo exceptuándose por número de ejemplares insuficiente a incisivos superiores e inferiores. Para la comparación de los diámetros entre las series se empleó ANOVA y test de Tukey como método post-hoc. Las series analizadas también se caracterizaron mediante la determinación de sus módulos para primeros y segundos molares superiores. Posteriormente se realizó Análisis de Componentes Principales a fin de evaluar la variabilidad presente y situar gráficamente las series en el contexto de la variación presentada. El ANOVA, con su posterior contrastación post-hoc, permitió establecer que las series se pueden diferenciar en función del diámetro mesio-distal de caninos superiores y segundos y terceros molares inferiores y, respecto del diámetro vestíbulo-lingual, según primeros y segundos premolares superiores, primeros y segundos molares superiores, y segundo y terceros molares inferiores. El análisis de componentes principales permitió observar que la mayor variabilidad queda explicada por las variables que describen la arcada dentaria inferior. La caracterización según los módulos dentales define a la serie Arroyo Seco 2 como hipermacrodonta para primeros y segundos molares, como mesodontaa la serie Rio Negro (según ambas piezas dentales), como macrodonta/microdonta a la serie Pampa Grande y como macrodonta/mesodonta a la serie Delta del Paraná.
ABSTRACT This paper compares the mesiodistal and buccolingual odontometric diameters in 63 male skulls, all with adult dentition, composed by four Argentinean skulls series: Arroyo Seco 2, Río Negro, Pampa Grande and Delta del Paraná. Almost all teeth were analyzed, with the exception of upper and lower incisors due to insufficient data. ANOVA and Tukey test, as a post-hoc method, were used in order to compare the diameters of dental crowns. The analyzed series were also characterized by determining their crown modules for first and second upper molars. Subsequently, Principal Component Analysis was performed in order to evaluate the existent variability and establish graphically the series in the variation context. ANOVA and Tukey post-hoc test established that the series could be mesiodistal diameter differentiated for upper canines and second and third lower molars. First and second premolars, first and second upper molars, and second and third lower molars differentiate variables for the buccolingual diameter. Principal components analysis show that most of the variability observed between the variables is related to the lower jaw. Molar crown modules define Arroyo Seco 2 series as hipermacrodontic for first and second upper molars, Río Negro series as mesodontic for both molars, Pampa Grande series as macrodontic/microdontic, and Delta del Paraná series as macrodontic / mesodontic.
RESUMEN Durante muchos siglos, la regulación del crecimiento de los órganos y los tejidos se relacionó con su función y con la temperatura, esta última se asociaba con la llegada de sangre al órgano. Con el surgimiento de la biología experimental y la endocrinología, en la segunda mitad del siglo XIX, comenzaron a realizarse experimentos para explicar el crecimiento de los tejidos. Se estableció por entonces el efecto estimulante de las hormonas. En la primera mitad del siglo XX, surgieron distintos modelos que proponían la existencia de estimulantes e inhibidores del crecimiento, tanto de acción local como general. A partir de 1962 se desarrolló el concepto de chalonas para referirse a inhibidores del crecimiento específicos de tejido pero no de especie, veinte años después el término cayó en el olvido para ser retomado recientemente, en una forma renovada. Con el descubrimiento de los factores de crecimiento, se demostró que las sustancias reguladoras son de acciones más variadas y complejas. El modelo actual de la regulación del crecimiento incluye numerosas sustancias de efectos y mecanismos de acción muy variados que a su vez están en relación con los efectos del medio ambiente.
ABSTRACT For many centuries, regulation of organ and tissue growth was thought to be related to function and temperature, the latter was associated with the arrival of blood to the organ. With the beginning of experimental biology and endocrinology, in the second half of the nineteenth century, the first experiments to explain tissue growth were carried out. By that time, the stimulant effect of hormones was established. In the first half of the twentieth century, different models that stated the existence of growth stimulants and inhibitors with local and general action arose. Since 1962, the concept of chalone was developed to refer to growth inhibitors specifi c of tissue but not of species. Twenty years later, the term was forgotten but it has been retaken with a new sense recently. With the discovery of growth factors, it was demonstrated that regulatory substances have complex and varied actions. The current model of growth regulation includes substances with a wide range of effects and action mechanisms that are integrated and responsive to the environment.
ABSTRACT Genomic and darwinian medicine deal with the application of hereditary and evolutionary principles for the understanding of health and disease. The progress in molecular and bioinformatics knowledge is making possible through a holistic approach to biological phenomena and one aspect of it, host-pathogen coevolution, is discussed with examples of research performed by our group. The search for the etiology of genetic diseases can focus on simple traits with mendelian inheritance or in more complex multifactorial characteristics, as well as in nuclear or mitochondrial DNA genes. Also important is the investigation of genetically conditioned variation in response to drugs (pharmacogenomics) and unorthodox environmental effects (epigenetics). Every day the genome of a given cell receives one million lesions which should be repaired. Defects in repair mechanisms can lead to diseases, one important category of them being neurological disorders. The association between intronic inversions which lead to severe hemophilia A and the prevalence of Factor VIII inhibitors in these patients was also considered using information obtained by the Porto Alegre group and those of colleagues living in other cities. The final message emphasizes the need for an evolutionary approach to fully understand pathologic processes and their management
Durante muchos siglos, la regulación del crecimiento de los órganos y los tejidos se relacionó con su función y con la temperatura, esta última se asociaba con la llegada de sangre al órgano. Con el surgimiento de la biología experimental y la endocrinología, en la segunda mitad del siglo XIX, comenzaron a realizarse experimentos para explicar el crecimiento de los tejidos. Se estableció por entonces el efecto estimulante de las hormonas. En la primera mitad del siglo XX, surgieron distintos modelos que proponían la existencia de estimulantes e inhibidores del crecimiento, tanto de acción local como general. A partir de 1962 se desarrolló el concepto de chalonas para referirse a inhibidores del crecimiento específi cos de tejido pero no de especie, veinte años después el término cayó en el olvido para ser retomado recientemente, en una forma renovada. Con el descubrimiento de los factores de crecimiento, se demostró que las sustancias reguladoras son de acciones más variadas y complejas. El modelo actual de la regulación del crecimiento incluye numerosas sustancias de efectos y mecanismos de acción muy variados que a su vez están en relación con los efectos del medio ambiente.