Communication and Signaling — Study Notes
Communication and Signaling – Study Notes
Learning context
Instructor mentioned learning objectives for today but did not list them explicitly; students should refer to the home materials for the stated objectives.
Administrative bits touched: poster/creative practice showcase (calls closed by the time of talk), postgraduate study information session (Sept 10, Taranga and Hamilton), a quick post-test questionnaire to help tailor teaching and study support, and schedule reminders about labs and Kingitanga holiday logistics.
What is communication?
Core idea: transmission of information between one or more senders and a receiver.
Signal: a product produced by an animal that has evolved to carry information and to affect the behavior of another animal (the receiver).
Receiver: the individual that perceives and responds to the signal.
When we discuss signals, we focus on information-carrying signals that have evolved to influence fitness-related outcomes.
Cue (contrast): information used by others that did not evolve for communication; it is incidental or byproduct-based.
Examples distinguishing signal vs cue:
CO₂ emission by mammals as a cue for mosquitoes seeking a blood meal (not evolved to signal mosquitoes).
Mouse running through a forest: noise can act as a cue for predators, but not a signal evolved for predator indication.
Why do animals communicate? Adaptive significance
Communicating can maximize fitness by influencing the receiver’s behavior in ways that benefit the signaler (and sometimes the receiver).
Potential functions of signals include:
Mating (courtship signals)
Foraging and food cues
Predation avoidance or deterrence
Play and social interactions
Aggression and territoriality
Modalities of communication include several channels; signals must have a selective advantage and be adaptive, not just incidental byproducts.
Examples of communicators and signals (overview)
Flame bowerbirds (visual courtship and display): male builds a bower, decorates with colors, performs a dance to attract a female.
Glowworms (bioluminescent visual signal): larvae produce light to lure prey; the ecological context creates an “ecological trap” for prey attracted to light.
Nautilus (olfactory/chemical signals): use chemical cues from female anal glands in a Y-maze to attract males; demonstrates chemical signal use in mate finding.
Toads (auditory signals): male croaks to attract females and to repel rival males; size-related pitch differences convey information about the male’s size.
Water striders (tactile/vibrational signals): use substrate-borne vibrations (leg movements) for courtship, mating, territoriality, or food defense.
Electric fish (electrical signals): use electric signals for species recognition, courtship, sex recognition, and competition (rarer modality).
Jumping spiders (multimodal courtship): male and female engage in signals across visual, tactile, and possibly olfactory channels; signals may be used for courtship, species recognition, and signaling quality.
Spotted hyenas (visual, olfactory, and social signals): pseudo-penis (enlarged clitoris) as a potential signal of testosterone/androgren levels and social dominance; observed in greeting ceremonies and associated with maternal rank and reproductive outcomes.
Visual signals (mode 1)
Common and conspicuous in mammals and birds; important channel across many taxa.
Glowworm bioluminescence: visual lure to attract prey; ecological trap context complicates cost-benefit for receivers (prey drawn to light may be eaten).
Bowerbird example highlights: bright colors, dances, and displays function as signals of mate quality (e.g., shininess, vigor).
Jumping spiders: elaborate visual displays; multimodal signaling (colorful legs, body, and movement) during courtship.
Hyena pseudo-penis often functions as a vivid visual cue of dominance/ testosterone status in greeting ceremonies.
Key point: multiple visual signals can provide redundancy, emphasize signal quality, and help in cluttered, leaf-litter-dense habitats where single cues could be obscured.
Olfactory/chemical signals (mode 2)
Nautilus example: male responsiveness to female chemical cues from anal glands demonstrates olfactory-based mate finding.
Significance: chemical signals can travel in water/air and persist across distances, enabling long-range or diffuse signaling.
In nautilus: adult males show attraction to female-derived chemical cues (juvenile males show less responsiveness).
Broader note: chemical signals can mediate mate attraction, species recognition, territory marking, and social communication in many taxa.
Auditory signals (mode 3)
Toads: croaks convey information about size and fighting ability; playback experiments used high-pitched (small) vs. low-pitched (large) calls to test aggression toward defenders.
Findings: medium-sized toads attacked more when presented with a high-pitched call from a small defender, indicating signal information modified behavior; large defender signals did not produce the same pattern, suggesting auditory cues combine with visual/tactile information in decision-making.
Takeaway: auditory signals can convey size or competitive ability, but full signaling often involves integration with other modalities.
Tactile and vibrational signals (mode 4)
Water striders: use leg-induced substrate vibrations to communicate for courtship, mating, territorial defense, and feeding cues.
Characteristics: pattern frequency and amplitude convey different messages; tactile signals can be crucial in environments where visual cues are limited or noisy.
Electrical signals (mode 5)
Some electric fishes produce electric fields or discharges to deter competitors, recognize conspecifics, or select mates.
Electrical signaling is relatively rare but can play a role in species, sex, and competitive recognition.
Multimodal signaling and ecological context
Jumping spiders and many other species often employ multiple simultaneous signals (visual + tactile + possible olfactory) to:
Increase recognition success in visually cluttered habitats.
Convey multiple aspects of signaler quality (e.g., health, vigor, species identity).
Provide fallback options if one channel is blocked or less effective in a given environment.
Environmental complexity and social context can favor redundancy and modality-specific information streams.
Case study: Jumping spiders (video discussion)
Male-female courtship displays involve multiple signal types (visual ornamentation, dance movements, leg signaling).
Olfactory signals may also contribute to mate finding, though visual cues are prominent.
Why multiple signals? to demonstrate signaler quality more robustly, to emphasize species identity, and to ensure signal is effective in cluttered habitats; if one modality fails, others may still succeed.
Spotted hyenas and the pseudo-penis (signal and physiology)
Anatomy and social structure
Hyenas exhibit a matriarchal social system with dominant females.
Female hyenas possess an enlarged clitoris forming a pseudo-penis; associated with high androgen/ testosterone levels.
Functional interpretations of the pseudo-penis
Hypothesis 1: Signal of dominance/ testosterone level (adaptive signal of status and aggressiveness).
Hypothesis 2: Associated with reproduction and labor challenges (dangerous during birth; cannot be explained solely as a signal).
The pseudo-penis could serve as a visual and olfactory indicator of hormonal state, contributing to social dynamics and hierarchical maintenance.
Greeting ceremony and social signaling
Subordinate female submits (flops down) while dominant female displays her pseudo-penis to reinforce hierarchy.
Signals during greeting include visual, tactile, and possibly olfactory cues.
Reproductive success and social rank
Higher maternal social status correlates with higher cub survival and earlier age at first reproduction for offspring.
Data show maternal rank tracks to daughter rank (intergenerational inheritance of social status).
Higher rank associated with greater androgen levels and greater aggression.
Cost considerations and hypotheses
Pseudopenus may be a costly, potentially dangerous feature during labor; its persistence suggests a benefit outweighing costs in social dominance and reproductive success.
Possible post-copulatory sperm competition or sperm choice implications are hypothesized but not conclusively proven.
Evolutionary questions
Is the pseudo-penis primarily a signal (honest indicator of testosterone and dominance), or a byproduct of androgen-driven development? Or both?
The observed signaling may function in multiple contexts (visual display, olfactory cues, social interaction) and contribute to fitness via dominance and reproductive access.
Honesty in signaling: how signals stay reliable
Why don’t animals “cheat” on signals? Two classic hypotheses:
Handicap hypothesis: signals are costly to produce; only high-quality individuals can afford them, making cheating unprofitable.
Index signal (cannot be faked): some traits are directly tied to physical attributes and cannot be faked regardless of investment.
Examples from the talk:
Toes example (index signal): larger vocal apparatus correlates with larger body size and lower croak frequency; this trait is costly or constrained by anatomy, making it difficult to fake.
Costly signaling and resource constraints (handicap example)
Stock-eyed flies: elaborate eye-stocks and ornamentation require substantial nutrition; high-quality individuals can afford them, while low-quality individuals cannot, keeping signals honest.
Social costs of bluffing (alternative honest signaling mechanism)
Wasps with bold face markings: larger markings correlate with dominance, but manipulation experiments show receivers react to manipulated signals (e.g., increased aggression toward fake dominant signals).
This demonstrates social enforcement of honesty: deceptive signals incur social costs, limiting their spread.
Takeaway about honesty mechanisms
Honest signals can be maintained by costs that are difficult to bear for low-quality individuals, or by social mechanisms that punish deception.
Deception and mimicry: looking ahead
The plan for tomorrow’s discussion includes deception and mimicry, i.e., how dishonest signaling and mimic signals evolve and under what ecological circumstances they persist.
Quick connections to theory and real-world relevance
Signaling theory underpins understanding of mating systems, competition, and social structure across taxa.
The discussed examples illustrate how multimodal signals can provide robust communication in complex environments.
Practical relevance includes insights for conservation biology (e.g., recognizing the importance of signaling modalities for mate finding or social cohesion) and for understanding how environmental changes might disrupt communication channels.
Experimental design takeaways from the transcript
Y-maze experiments (nautilus): test for directional chemical cue preference by presenting two chemical treatments.
Playback and manipulation studies (toads): test how auditory signals interact with visual cues to influence aggression and mating decisions.
Vibrational signaling studies (water striders): analyze frequency and amplitude to determine signaling function.
Social manipulation experiments (wasps): test honesty and social responses to altered signals to understand costs of bluffing.
Key formulas and concepts (typical signaling theory representations)
Honest signaling condition (basic intuition):
For a signal with benefit B to the sender and cost C(s, q) to produce signal strength s given sender quality q, honesty can be maintained if
C(s, q{high}) \,\le\, B \text{and} \ C(s, q{low}) \,>\, B.Index signal (unfakable trait):
Signal strength s is a function of an underlying, non-modifiable trait q: s = h(q)\quad\text{with } h\text{ monotone and not easily altered by behavior}.
Multimodal signaling rationale (conceptual):
When multiple channels convey information about quality, a mismatch across modalities can be costly for a deceptive signaler and may enhance detection by the receiver.
Summary of takeaways for exam prep
Understand the distinction between signals (evolved, fitness-relevant communication) and cues (non-evolved information use).
Be able to categorize signaling modalities and give at least one example per modality from the lecture (visual: bowerbirds/bioluminescent glowworms; olfactory: nautilus; auditory: toads; tactile: water striders; electrical: some fishes; multimodal: jumping spiders; social signaling: hyenas).
Explain why signaling can increase fitness, including mating success and competitive outcomes.
Describe the handicap and index signal hypotheses and apply them to examples (stock-eyed flies for handicap; toad vocalization as index trait; social costs in wasps as enforcement).
Discuss the concept of ecological traps in signaling (glowworms) and how contexts can influence the adaptive value of signals for receivers.
Explain how social structure and hormones (e.g., androgen levels in hyenas) can influence signaling traits and fitness outcomes.
Recognize experimental approaches used to study signaling (Y-maze, playback studies, vibrational analysis, manipulation of visual cues) and the kinds of conclusions they can support.
Practical takeaways for class and labs
Expect discussion on deception and mimicry in tomorrow’s session.
Friday obligatory lab will cover data prepping; subsequent lab will cover data analysis.
Note schedule adjustments around Kingitanga; plan for next class accordingly.
Quick 참고 (connections to broader themes)
Signals act as honest indicators of quality in many systems, reinforcing the idea of sexual selection and social hierarchies.
The evolution of signaling is tightly linked to receiver psychology, ecological constraints, and the costs/benefits balance for signalers.
Real-world relevance includes interpreting animal behavior in the wild, designing conservation strategies that respect communication channels, and understanding how anthropogenic changes might disrupt critical signals.