BI2CV1 - Lecture 4 - Form and Function PDF

Form and function BI2CV1 Comparative Vertebrate Biology Dr Manabu Sakamoto [email protected] Recap: Vertebrate body plan (bauplan) Segmented brain Cranium Dorsal neural tube Notochord Pharynx Heart Segmented muscles Sensory/visual organs (paired)...

Form and function BI2CV1 Comparative Vertebrate Biology Dr Manabu Sakamoto [email protected] Recap: Vertebrate body plan (bauplan) Segmented brain Cranium Dorsal neural tube Notochord Pharynx Heart Segmented muscles Sensory/visual organs (paired) Martinez-Morales 2016. Brief Funct Genomics 15: 315-321 Vertebrate body plan (bauplan) This vertebrate body plan is observed across vertebrates during the phylotypic stage of embryonic development. Morphological diversity of embryos converges towards this conserved body plan, then diverges again: The “hourglass model”. Martinez-Morales 2016. Brief Funct Genomics 15: 315-32 Early vertebrate evolution Paired Paired pectoral pelvic fins fins Placoderms Ossified endoskeleto ns Donoghue & Keating 2014. Palaeontology 57: 879–893 Placoderms By Kylinxia - Own work, CC BY-SA 4.0 By Jobbins et al. CC BY 4.0 By Epipelagic - Own work, CC BY-SA 3.0 By Russell K. Engelman - Engelman, CC BY 4.0 By Entelognathus - Own work, CC BY-SA 4.0 Chondrichthyes: Cartilaginous fishes By Epipelagic - Own work, CC BY-SA 3.0 Osteichthyes: Bony fishes Fully ossified endoskeleton. Actinopterygii Ray-finned fishes Sarcopterygii Lobe-finned fishes By Prehistoricplanes - Own work, CC BY-SA 4.0 Guiyu oneiros, one of the earliest bony fishes from the Late Silurian, 425 Mya By ArthurWeasley - Own work, CC BY 3.0 Actinopterygii: Ray-finned fishes Bony ray-fins Muscles controlling fins are located within the body The most diverse vertebrate clade (50% of all vertebrates)! By Epipelagic - Own work, CC BY-SA 3.0 Sarcopterygii: lobe-finned fishes Fins at the ends of short bony appendages. Fins are controlled by muscles on the appendages. Coelacanths have been By Henderson et al. CC BY 4.0 observed “walking” on the ocean floor. By Lionel Cavin et al., CC BY 4.0 Sarcopterygii: lobe-finned fishes Three modern clades: Dipnoi (Lungfish) Actinistia (Coelacanths) Tetrapoda (four-limbed vertebrates) Non-tetrapod lobe-finned fishes are not diverse as ray-finned fishes but higher diversity in fossil record. By Tim Evanson, CC BY-SA 2.0 Zhao et al. 2021. Science China. Life Sciences 6 Tetrapodomorpha: tetrapods and relatives Gardner et al. 2019. Comptes Rendus Palevol 18 Ahlberg 2018. Earth Envrion Sci Trans R Soc Edinb 109: 115-137 Tetrapoda Sarcopterygians with four limbs (two pairs of limbs) Forelimb Humerus, radius, ulna, manus Hindlimb Femur, tibia, fibula, pes By Auckland War Memorial Museum, CC BY 4.0 Tetrapod body plan Cranial skeleton Skull and mandible Axial skeleton Cervical vertebra Cervical vertebrae e Thoracic/dorsal vertebrae Thoracic Sacral vertebrae vertebra e Caudal vertebrae Appendicular skeleton Limbs and girdles Caudal vertebra e Sacral vertebra e Tetrapod body plan diversity Tetrapod body plan diversity Adaptations and body plans Vertebrate morphology We’ve largely But we haven’t covered what delved into why vertebrates look vertebrates look like. the way they do. Form and function Taxonomy Who are they? Adaptatio Adaptatio n n What do they look Form Selectio like? n What are they Function doing? Selectio Selectio n n What do they need Ecology to do? Where do they Environment live? The laws of physics and body plans Vertebrates are subjected to the laws of physics. Interaction with physical medium (e.g., water, air) changes with scale. Body plans reflect adaptations within the confines of or to overcome physical restrictions. Gazzola et al. 2014. Nature Physics 10: 758-761 Physical constraints on body plans Larger sizes are beneficial for various reasons. Escape predation Prey on smaller animals Larger sizes are also associated with challenges. Stronger effects of gravity. Not to Higher forces involved in scale! motion and impacts. Higher energy consumption. Adaptations at different scale Transitions between environmental regimes necessitate changes to gross morphology (body shape) and various traits. Change in size Change in shape in response to changes in effects of drag, gravity Aquatic to terrestrial habitats Changes in respiration, locomotion, support Martinez-Morales 2016. Brief Funct Genomics 15: 315-321 Liao 2022. Curr Biol 32: R666–71 Ahlberg 2018. Earth Envrion Sci Trans R Soc Edinb 109: 115-1 Scaling: Theoretical expectations of changes in size  Scaling factor Expected scaling relationships between physical measures when maintaining isometry (equal proportions). Area: V ∝ L2 or L ∝ A1/2 Volume: V ∝ L3 or L ×2 Length L 2L ∝ V1/3 ×k V ∝ L3 A ∝ L2 ×4 A2 = 6(2L)2 Area A = 6L2 Value = 24L2 ×k2 V A ×8 VolumeV = L3 V2 = (2L)3 ×k3 = 8L3 L where k is some scaling factor  Scaling factor Expected In biology,scaling we are often interested in between relationships how physical measures various physical when maintaining measures scale with isometry (equal body mass. proportions). Area: V ∝ L2 or L ∝ A1/2 Volume: V ∝ L3 or L ×2 Length L 2L ∝ V1/3 ×k V ∝ L3 A ∝ L2 ×4 A2 = 6(2L)2 Area A = 6L2 Value = 24L2 ×k2 V A ×8 VolumeV = L3 V2 = (2L)3 ×k3 = 8L3 L where k is some scaling factor Scaling factor We also tend to use a log- scale, which converts a multiplicative series into Linear relationship an additive one. between a measure of interest and This allows us to deal with body mass linear relationships rather than exponential ones. It’s just easier to interpret! Log- scale Expected scaling relationships in biology Length with mass L ∝ M1/3 Area with mass A ∝ M2/3 Gradient or L∝A 1/2 |L∝M 1/3 Gradient or slope should be 2/3 Length slope should Area be 1/3 2 Other measures of 1 3 3 interest will have their own scaling Mass Mass expectations! Expected scaling relationships in biology Isometry: Positive Isometr y Two measures scale in proportion to allometr y each other under theoretical expectations. Allometry: One measure scales disproportionately to another Negativ compared to theoretical expectations. e allometr Positive allometry: y More than expected Negative allometry: Less than expected Scaling in biology Scaling relationships in Expected slope for mass vs mass is 1 biology are very often allometric. Slope >1 Positive allometry Slopes