Domain: Natural Science — Morphology
Target concept: Sexual dimorphism in Xiphophorus (sword-bearing swordtail species): mature males develop an elongated, sword-like extension of the caudal fin, while females retain a rounded caudal fin.

Video generation prompt: Two African swordtails are displayed side by side, with a female on the left and a male on the right. Observe and compare the morphological differences between these two African swordtails.

Evaluation guide:
(i) Target concept: Visual identification of sexually dimorphic caudal fin morphology in Xiphophorus (the sword-bearing swordtail genus) as a binary phenotypic marker.
Minimum mechanism: The sword trait is genetically determined, developmentally fixed in males post-maturation, and anatomically distinct from female fin shape; no environmental induction or reversible plasticity affects its presence/absence in adult specimens.
(ii)Storyline: Frame 1–100 (10s): Fixed frontal-lateral view establishes stable spatial frame; left fish enters view fully visible with rounded caudal fin; right fish enters view fully visible with sword-like caudal fin; both remain motionless or exhibit only minor, synchronous undulation (no bending obscuring fin shape); viewer perceives contrast immediately due to unoccluded, co-visible, same-scale presentation; no camera motion or lighting transition disrupts comparative observation.

Manual:
Experimental Procedure
1. Position two live swordtails of the genus Xiphophorus — one mature female, one mature male — side-by-side in a clear, shallow aquarium with uniform backlighting.
2. Capture a 10-second static lateral-view video showing both fish simultaneously, centered horizontally, with no movement or zoom.
Observation of Experimental Phenomena
The female (left) displays a smoothly rounded caudal fin; the male (right) displays an elongated, sword-like caudal fin extending posteriorly beyond the body axis.
Summary of Experimental Principles
Sexual dimorphism in sword-bearing Xiphophorus swordtails: Males possess a sword-like caudal fin used in courtship; females possess a rounded caudal fin — a fixed, heritable morphological trait distinguishing the sexes.

Prompt Grounding rubric:
level_1: No two African swordtails present; or only one fish shown; or fish not identifiable as Xiphophorus africanus; or spatial arrangement absent (no side-by-side configuration); or gender assignment missing or unidentifiable (no left/right labeling or visual distinction implying female/male).
level_2: Two fish are present and placed side-by-side, but at least one is misidentified by gender (e.g., both appear with swords or both with rounded caudal fins); or spatial orientation is inconsistent (e.g., one fish faces away, rotated vertically, or occluded such that caudal fin shape cannot be assessed); or no stable fixed viewpoint: camera pans/zooms/rotates during display.
level_3: Two African swordtails are displayed side-by-side in a fixed, frontal, static view: one on the left, one on the right; both fully visible from lateral perspective; caudal fins are visually discernible; gender assignment is *implied* by morphology (left fish has rounded caudal fin, right fish has elongated sword-like caudal fin); no explicit labels required.
level_4: All conditions for score 3 are satisfied, AND both fish exhibit species-typical body shape (streamlined, laterally compressed), dorsal/anal fin placement consistent with Xiphophorus africanus, and no extraneous objects (e.g., tanks, plants, text overlays) interfere with morphological comparison.
level_5: All conditions for score 4 are satisfied, AND both fish maintain identical posture (horizontal swimming alignment), same scale (no size distortion between left and right), same lighting direction and intensity across both subjects, and no motion blur or frame duplication affecting caudal fin shape perception.

Scientific and Causal Correctness rubric:
level_1: Caudal fin morphology contradicts biological fact: e.g., left fish (intended female) displays a sword-like caudal fin, OR right fish (intended male) displays a rounded caudal fin; OR both fins are identical in shape; OR caudal fin shape is ambiguous due to deformation, transparency, or occlusion.
level_2: At least one fish displays a caudal fin shape inconsistent with sexual dimorphism in Xiphophorus africanus (i.e., male lacks sword, female lacks roundedness), AND no other morphological features support correct sex assignment; OR presence of non-biological features (e.g., artificial appendages, unnatural coloration not found in wild-type X. africanus) undermines causal validity.
level_3: Left fish exhibits a clearly rounded caudal fin; right fish exhibits a clearly elongated, sword-like caudal fin extending beyond the dorsal and anal fin base; both fins are solidly opaque and anatomically attached; no intermediate or hybrid morphology appears.
level_4: All conditions for score 3 are satisfied, AND both fish show no secondary sexual traits inconsistent with X. africanus (e.g., no gonopodium distortion in male, no gravid spot misplacement in female), AND caudal fin shape difference is the *only* visually dominant morphological contrast: no competing misleading traits (e.g., false sword in female due to injury artifact).
level_5: All conditions for score 4 are satisfied, AND the sword-like caudal fin in the male terminates in a natural taper (not blunt, forked, or frayed), AND the rounded caudal fin in the female shows smooth, symmetrical curvature without notches or asymmetry, AND both fins maintain natural pigmentation continuity with body (no abrupt color breaks at fin base).

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal violation: e.g., fish teleport between frames; one fish disappears/reappears; sudden scaling jump; caudal fin shape flickers between sword/rounded within same fish; lighting shifts abruptly mid-sequence.
level_2: Moderate violation: e.g., intermittent occlusion of caudal fin (e.g., tail bends behind body then reappears unchanged); visible stitching or layering artifacts between left/right fish; inconsistent shadow direction or cast between fish; visible frame drop causing discontinuous stillness.
level_3: Both fish remain continuously visible in fixed positions throughout; no teleportation, scaling change, or rotation; caudal fin shapes remain stable and unchanging; lighting and shadow are consistent across both subjects; no structural tearing or warping of fish anatomy.
level_4: All conditions for score 3 are satisfied, AND motion (if any minimal swimming motion is present) is smooth and synchronous between both fish; no inter-frame jitter or edge shimmer; no parallax shift indicating unstable viewpoint; background remains static and uniformly blurred or neutral.
level_5: All conditions for score 4 are satisfied, AND zero inter-frame inconsistency: every frame shows identical spatial registration of left/right fish relative to each other and to frame edges; no micro-wobble, no breathing motion artifact in fins, no subtle warping at fin tips across frames; perfect temporal stability of all morphological boundaries.