Developmental Constraints: Why St. Bernards Often Have an Extra Digit and Poodles Never Do

1985 ◽  
Vol 126 (3) ◽  
pp. 430-433 ◽  
Author(s):  
Pere Alberch
Keyword(s):  
Developmental Constraints ◽  
Extra Digit

scholarly journals Cost of autotomy drives ontogenetic switching of anti-predator mechanisms under developmental constraints in a land snail

2012 ◽  
Vol 279 (1748) ◽  
pp. 4811-4816 ◽  
Author(s):  
Masaki Hoso
Keyword(s):  
High Efficiency ◽  
Shell Growth ◽  
Land Snail ◽  
Life History Strategies ◽  
Body Parts ◽  
Developmental Constraint ◽  
Developmental Constraints ◽  
Evolution Of Life ◽  
Snake Range ◽  
In The Wild

Autotomy of body parts offers various prey animals immediate benefits of survival in compensation for considerable costs. I found that a land snail Satsuma caliginosa of populations coexisting with a snail-eating snake Pareas iwasakii survived the snake predation by autotomizing its foot, whereas those out of the snake range rarely survived. Regeneration of a lost foot completed in a few weeks but imposed a delay of shell growth. Imprints of autotomy were found in greater than 10 per cent of S. caliginosa in the snake range but in only less than 1 per cent out of it, simultaneously demonstrating intense predation by the snakes and high efficiency of autotomy for surviving snake predation in the wild. However, in experiments, mature S. caliginosa performed autotomy less frequently. Instead of the costly autotomy, they can use defensive denticles on the inside of their shell apertures. Owing to the constraints from the additive growth of shells, most pulmonate snails can produce these denticles only when they have fully grown up. Thus, this developmental constraint limits the availability of the modified aperture, resulting in ontogenetic switching of the alternative defences. This study illustrates how costs of adaptation operate in the evolution of life-history strategies under developmental constraints

Within and among plant variation in seed mass and pappus size in Tragopogon dubious

1989 ◽  
Vol 67 (5) ◽  
pp. 1298-1304 ◽  
Author(s):  
Mark A. McGinley
Keyword(s):  
Salt Lake ◽  
Salt Lake City ◽  
Seed Mass ◽  
Developmental Constraints ◽  
Position Effects ◽  
Plant Variation ◽  
Selection For ◽  
Lake City ◽  
Total Seed ◽  
Stalk Length

Individual seed mass of two seed morphs of Tragopogon dubious (L.) varied among plants and within and among flowering heads within individual plants growing near Salt Lake City, UT. Seeds of the light morph from the center of a receptacle were smaller than outer seeds, suggesting that variation in seed mass within heads was due to position effects. The total seed mass per head, seed number per head, and mean seed mass per head of both morphs declined in most plants over the season. Heads with larger total seed mass contained larger seeds both within and between plants so seasonal patterns in seed mass may be influenced by seasonal variation in the amount of resources available for investment in seeds. Seeds of the light colored morph had a greater dispersal potential than seeds from the dark colored morph because their disk loading was lower. Pappus size (both pappus radius and stalk length) increased with the number of seeds per head which may increase the efficiency of packaging fruits on the receptacle. Heads with a larger total seed mass allocated a smaller proportion of their resources to the dark seed morph which may serve to decrease the level of sibling competition experienced by the less dispersing seed morph. Thus, variation in investment in offspring may arise as a combination of developmental constraints and selection for variable investment.

scholarly journals Developmental constraints of quadrupedal coordination across crawling styles in human infants

2012 ◽  
Vol 107 (11) ◽  
pp. 3050-3061 ◽  
Author(s):  
Susan K. Patrick ◽  
J. Adam Noah ◽  
Jaynie F. Yang
Keyword(s):  
Nervous System ◽  
Stance Phase ◽  
Swing Phase ◽  
Interlimb Coordination ◽  
Young Age ◽  
Developmental Constraints ◽  
Human Infants ◽  
Coordination Patterns ◽  
Duration Of Cycle ◽  
Developing Nervous System

Human infants can crawl using several very different styles; this diversity appears at first glance to contradict our previous findings from hands-and-knees crawling, which suggested that there were strict limitations on coordination, imposed either mechanically or by the developing nervous system. To determine whether coordination was similarly restricted across crawling styles, we studied free crawling overground in 22 infants who used a number of different locomotor strategies. Despite the wide variety in the use of individual limbs and even the number of limbs used, the duration of the stance phase increased with duration of cycle, whereas the duration of the swing phase remained more constant. Additionally, all infants showed organized, rhythmic interlimb coordination. Alternating patterns (e.g., trotlike) predominated (86% of infants). Alternatively, yet much less frequently, all limbs used could work in synchrony (14% of infants). Pacelike patterns were never observed, even in infants that crawled with the belly remaining in contact with the ground so that stability was not a factor. To explore the robustness of the interlimb coordination, a perturbation that prolonged swing of the leg was imposed on 14 additional infants crawling on hands and knees overground or on the treadmill. The perturbation led to a resetting of the crawling pattern, but never to a change in the coordination of the limbs. The findings concur with those regarding other infant animals, together suggesting that the nervous system itself limits the coordination patterns available at a young age.

scholarly journals Dental tissue proportions in fossil orangutans from mainland Asia and Indonesia

2011 ◽  
Vol 1 (1) ◽  
pp. e1 ◽  
Author(s):  
Tanya M. Smith ◽  
Anne-Marie Bacon ◽  
Fabrice Demeter ◽  
Ottmar Kullmer ◽  
Kim Thuy Nguyen ◽  
...  
Keyword(s):  
Fossil Record ◽  
Homo Sapiens ◽  
Homo Erectus ◽  
Dental Tissue ◽  
Developmental Constraints ◽  
Enamel Thickness ◽  
Selective Pressures ◽  
The Past ◽  
Geometric Scaling ◽  
Dental Reduction

Orangutans (Pongo) are the only great ape genus with a substantial Pleistocene and Holocene fossil record, demonstrating a much larger geographic range than extant populations. In addition to having an extensive fossil record, Pongo shows several convergent morphological similarities with Homo, including a trend of dental reduction during the past million years. While studies have documented variation in dental tissue proportions among species of Homo, little is known about variation in enamel thickness within fossil orangutans. Here we assess dental tissue proportions, including conventional enamel thickness indices, in a large sample of fossil orangutan postcanine teeth from mainland Asia and Indonesia. We find few differences between regions, except for significantly lower average enamel thickness (AET) values in Indonesian mandibular first molars. Differences between fossil and extant orangutans are more marked, with fossil Pongo showing higher AET in most postcanine teeth. These differences are significant for maxillary and mandibular first molars. Fossil orangutans show higher AET than extant Pongo due to greater enamel cap areas, which exceed increases in enamel-dentine junction length (due to geometric scaling of areas and lengths for the AET index calculation). We also find greater dentine areas in fossil orangutans, but relative enamel thickness indices do not differ between fossil and extant taxa. When changes in dental tissue proportions between fossil and extant orangutans are compared with fossil and recent Homo sapiens, Pongo appears to show isometric reduction in enamel and dentine, while crown reduction in H. sapiens appears to be due to preferential loss of dentine. Disparate selective pressures or developmental constraints may underlie these patterns. Finally, the finding of moderately thick molar enamel in fossil orangutans may represent an additional convergent dental similarity with Homo erectus, complicating attempts to distinguish these taxa in mixed Asian faunas. 

scholarly journals How development affects evolution

2021 ◽  
Author(s):  
Mauricio González-Forero ◽  
Andy Gardner
Keyword(s):  
Niche Construction ◽  
Fitness Landscape ◽  
Stabilizing Selection ◽  
Mathematical Framework ◽  
Phenotypic Evolution ◽  
Landscape Development ◽  
Developmental Constraints ◽  
Evolutionary Pathway ◽  
Punctuated Equilibria ◽  
Adaptive Radiations

How development affects evolution. A mathematical framework that explicitly integrates development into evolution has recently been derived. Here we use this framework to analyse how development affects evolution. We show that, whilst selection pushes genetic and phenotypic evolution uphill on the fitness landscape, development determines the admissible evolutionary pathway, such that evolutionary outcomes occur at path peaks, which need not be peaks of the fitness landscape. Development can generate path peaks, triggering adaptive radiations, even on constant, single-peak landscapes. Phenotypic plasticity, niche construction, extra-genetic inheritance, and developmental bias variously alter the evolutionary path and hence the outcome. Selective development, whereby phenotype construction may point in the adaptive direction, may induce evolution either towards or away landscape peaks depending on the developmental constraints. Additionally, developmental propagation of phenotypic effects over age allows for the evolution of negative senescence. These results help explain empirical observations including punctuated equilibria, the paradox of stasis, the rarity of stabilizing selection, and negative senescence, and show that development has a major role in evolution.

scholarly journals Modular marvels: The ecology, evolvability, and energetics of bryozoan polymorphism

2021 ◽  
Author(s):  
◽  
Carolann Schack
Keyword(s):  
New Zealand ◽  
Community Assembly ◽  
Environmental Conditions ◽  
Environmental Filtering ◽  
Classification Systems ◽  
Energetic Cost ◽  
Developmental Constraints ◽  
Mechanical Advantage ◽  
Colony Form ◽  
Hard Substrata

<p>Modularity is a fundamental concept in biology. Most taxa within the colonial invertebrate phylum Bryozoa have achieved division of labor through the development of specialized modules (polymorphs), and this group is perhaps the most outstanding exemplar of the phenomenon. This thesis addresses several gaps in the literature concerning the morphology, ecology, energetics, and evolvability of bryozoan polymorphism.  It has been over 40 years since the last review of bryozoan polymorphism, and here I provide a comprehensive update that describes the diversity, morphology, and function of bryozoan polymorphs and the significance of modularity to their evolutionary success. While the degree of module compartmentalization is important for the evolution of polymorphism in bryozoans, this does not appear to be the case for other colonial invertebrates.  To facilitate data collection, I developed a classification system for polymorphism in cheilostome bryozoans. While classification systems exist for bryozoan colony form, the system presented here is the first developed for polymorphism. This system is fully illustrated and non-hierarchical, enabling swift classification and statistical comparisons at many levels of detail.  Understanding community assembly is a key goal in community ecology, but previous work on bryozoan communities has focused on colony form rather than polymorphism. Environmental filtering influences community assembly by excluding ill-adapted species, resulting in communities with similar functional traits. An RLQ (a four-way ordination) analysis incorporating spatial data was run on a dataset of 642 species of cheilostomes from 779 New Zealand sites, to investigate environmental filtering of colony form and zooid polymorphism. This revealed environmental filtering of colony form: encrusting-cemented taxa were predominant in shallow environments with hard substrata (200 m). Furthermore, erect taxa found in shallow environments with high current speeds were typically jointed. Surprisingly, polymorphism also followed environmental gradients. External ovicells (brood chambers) were more common in deeper, low oxygen water than immersed and internal ovicells. This may reflect the oxygen needs of the embryo or increased predation intensity in shallow environments. Bryozoans with costae (rib-like spines) tended to be found in deeper water as well, while bryozoans with calcified frontal shields were found in shallow environments with a higher concentration of CaCO₃. Avicularia (defensive grasping structures) were not related to environmental conditions, and changes in pivot bar structure with depth likely represent a phylogenetic signal. Factors influencing community assembly were somewhat partitioned by levels of organization, since colony form responds to environmental conditions, while the effects of evolutionary history, predation, and environmental conditions were not well-separated for zooid-level morphology. Finally, rootlets may have been a key innovation that allowed cementing taxa to escape hard substrata, potentially contributing to the cheilostome radiation.  Despite the diversity of life on earth, many morphologies have not been achieved. Morphology can be limited by a variety of constraints (developmental, historical, biomechanical) and comparing the distribution of realized forms in a theoretical form-space (i.e. “morphospace”) can highlight which constraints are at play and potential functions. If traits cluster around biomechanical optima, then morphology may be shaped by strong selective pressures. In contrast, a well-explored (filled) morphospace suggests weak constraints and high morphological evolvability. Here, constraints on morphospace exploration were examined for 125 cheilostome bryozoan species from New Zealand. The mandible morphospaces for avicularia (beak-like polymorphs) were visualized using Coordinate-Point Extended Eigenshape analysis. Mechanical advantage, moment of inertia, drag, peak force, and rotational work required to close the mandible were calculated for theoretical (n=47) and real mandibles (n=224) to identify biomechanical optima. The volume and surface of area of the parcel of water passed through by the closing mandible (referred to as the “domain”) was also calculated. The theoretical morphospace of avicularia is well-explored, suggesting they are highly evolvable and have relaxed developmental constraints. However, there may be constraints within lineages. A well-developed fulcrum (complete pivot bar) may be an evolutionary pre/corequisite to evolving mandibles with extreme moments of inertia such as setose and highly spathulate forms. The most common mandible shape, triangular, represents a trade-off between maximizing domain size, minimizing energetic cost (force and construction material), and minimizing the potential for breakage. This suggests that they are well suited for catching epibionts, representing the first empirical evidence for avicularian function. Tendon length and mechanical advantage are limited by tendon width, which itself is constrained by the base width of the mandible. This explains the low mechanical advantage of setose mandibles and suggests that they are unable to grasp epibionts. The calories required to close the mandible of an avicularium (estimated from rotational work) are quite small (1.24 x 10⁻¹⁶ to 8.82 x 10⁻¹¹ cal).  Overall, this thesis highlights the complexity of bryozoan polymorphism and suggests cheilostome avicularia could provide a unique evolutionary system to study due to their apparent lack of strong developmental constraints. Future studies into the ecology of polymorphism should focus on the degree of investment (polymorph abundance within a colony) rather than presence or absence.</p>

The naked ape as an evolutionary model, 50 years later

2018 ◽  
Vol 68 (3) ◽  
pp. 227-246
Author(s):  
Nico M. van Straalen
Keyword(s):  
Natural Selection ◽  
Evolutionary Biology ◽  
Evolutionary Model ◽  
Developmental Constraints ◽  
Body Hair ◽  
Product Evolution ◽  
Adaptive Explanation ◽  
History Of ◽  
Popular Texts ◽  
The Brain

AbstractEvolution acts through a combination of four different drivers: (1) mutation, (2) selection, (3) genetic drift, and (4) developmental constraints. There is a tendency among some biologists to frame evolution as the sole result of natural selection, and this tendency is reinforced by many popular texts. “The Naked Ape” by Desmond Morris, published 50 years ago, is no exception. In this paper I argue that evolutionary biology is much richer than natural selection alone. I illustrate this by reconstructing the evolutionary history of five different organs of the human body: foot, pelvis, scrotum, hand and brain. Factors like developmental tinkering, by-product evolution, exaptation and heterochrony are powerful forces for body-plan innovations and the appearance of such innovations in human ancestors does not always require an adaptive explanation. While Morris explained the lack of body hair in the human species by sexual selection, I argue that molecular tinkering of regulatory genes expressed in the brain, followed by positive selection for neotenic features, may have been the driving factor, with loss of body hair as a secondary consequence.

scholarly journals Neural network detected in a presumed vestigial trait: ultrastructure of the salmonid adipose fin

2011 ◽  
Vol 279 (1728) ◽  
pp. 553-563 ◽  
Author(s):  
J. A. Buckland-Nicks ◽  
M. Gillis ◽  
T. E. Reimchen
Keyword(s):  
Evolutionary Biology ◽  
Primary Cilia ◽  
Free Edge ◽  
Energetic Cost ◽  
Developmental Constraints ◽  
Fisheries Science ◽  
Adipose Fin ◽  
First Time ◽  
Two Sides ◽  
Turbulent Water

A wide variety of rudimentary and apparently non-functional traits have persisted over extended evolutionary time. Recent evidence has shown that some of these traits may be maintained as a result of developmental constraints or neutral energetic cost, but for others their true function was not recognized. The adipose fin is small, fleshy, non-rayed and located between the dorsal and caudal fins on eight orders of basal teleosts and has traditionally been regarded as vestigial without clear function. We describe here the ultrastructure of the adipose fin and for the first time, to our knowledge, present evidence of extensive nervous tissue, as well as an unusual subdermal complex of interconnected astrocyte-like cells equipped with primary cilia. The fin contains neither adipose tissue nor fin rays. Many fusiform actinotrichia, comprising dense striated macrofibrils, support the free edge and connect with collagen cables that link the two sides. These results are consistent with a recent hypothesis that the adipose fin may act as a precaudal flow sensor, where its removal can be detrimental to swimming efficiency in turbulent water. Our findings provide insight to the broader themes of function versus constraints in evolutionary biology and may have significance for fisheries science, as the adipose fin is routinely removed from millions of salmonids each year.

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